- Email: [email protected]
Can fishes resolve temporal characteristics of sounds? New insights using auditory brainstem responses
Hearing Research 169 (2002) 36^46 www.elsevier.com/locate/heares
Can ¢shes resolve temporal characteristics of sounds? New insights using auditory brainstem responses Lidia Eva Wysocki , Friedrich Ladich Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria Received 14 November 2001; accepted 31 January 2002
Abstract Numerous fish species produce broad-band pulsed sounds with a distinct temporal patterning which is thought to be important during intraspecific communication. In order to determine whether fishes are able to utilize temporal characteristics of acoustic signals, time resolution was determined in four species of otophysines and anabantoids by analyzing auditory brainstem responses (ABRs) to double-click stimuli with varying click periods. At click periods of 3.5 ms, two distinct ABRs were clearly detectable in all species. The minimum pulse period resolvable by the auditory system was below 1.5 ms in each species and slightly intensitydependent. No differences were found between vocal and non-vocal species within each taxon. Comparisons of the time resolution data to the pulse periods of intraspecific sounds in the vocal species showed that the otophysine Platydoras costatus and the anabantoid Trichopsis vittata are likely to process each pulse within a series of intraspecific sounds. However, as non-vocal and vocal species have a similar minimum resolvable click period, the high temporal resolution capacities of the auditory system of fish might not represent special adaptations for intraspecific acoustic communication. Nonetheless, we suggest that temporal characteristics of naturally occurring conspecific and heterospecific sounds provide reliable information for acoustic communication. 4 2002 Elsevier Science B.V. All rights reserved. Key words: Auditory temporal resolution; Auditory brainstem response; Teleost ; Temporal sound pattern; Acoustic communication
1. Introduction Sound production is widespread among ¢shes and occurs in various contexts such as in distress situations or during social interactions. Acoustic signals play a role in the mating systems of several groups such as damsel¢shes (Myrberg et al., 1986), sun¢shes (Gerald, 1971), toad¢shes (McKibben and Bass, 1998), mormyrids (Crawford, 1997), and cat¢sh (Pruzsinszky and Ladich, 1998) as well as during agonistic interactions (for a review see Ladich, 1997a). Information transmitted by
* Corresponding author. Tel.: +431 4277 54515; Fax: +431 4277 9544. E-mail address: [email protected] (L.E. Wysocki). Abbreviations: ABR, auditory brainstem response; BM, body mass; HL, hearing level; SL, standard length; SPL, sound pressure level
acoustic signals could be encoded by their frequency, intensity, or temporal content. Fish sounds often consist of series of short broadband pulses (e.g., stridulatory sounds of gouramis and cat¢shes; Ladich et al., 1992; Ladich, 1997b) with distinct temporal patterns, whereby interpulse intervals vary from only a few up to several dozen milliseconds (Myrberg et al., 1978; Ladich et al., 1992; Pruzsinszky and Ladich, 1998). Therefore, several researchers have suggested that ¢sh sounds code information in the time rather than frequency domain (Winn, 1964, 1967; Myrberg et al., 1978). Winn (1964) demonstrated that temporal properties of sounds such as unit duration and repetition rate play a decisive role in the communication system of the oyster toad¢sh Opsanus tau. Courtship sounds in closely related species of sun¢shes (Gerald, 1971), pomacentrids (Myrberg et al., 1986), mormyrids (Marvit and Crawford, 2000), as well as calls of various vocal gadoid ¢sh mainly di¡er in their
0378-5955 / 02 / $ ^ see front matter 4 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 5 9 5 5 ( 0 2 ) 0 0 3 3 6 - 2
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
temporal patterning (Hawkins and Rasmussen, 1978). In the haddock Melanogrammus aegle¢nus, the distinct sounds produced in various contexts di¡er in terms of their structure in the time domain. Temporal patterns of sounds, namely the pulse period, proved to be the most important factor for species recognition in damsel¢shes (Myrberg and Spires, 1972). Furthermore, Mann and Lobel (1997) demonstrated that during sound propagation the most reliable information is transferred by the pulse period of damsel¢sh sounds. Considering the assumed importance of temporal patterns in sound communication, surprisingly little is known about the temporal resolution abilities of the auditory system of ¢shes. A recent study (Marvit and Crawford, 2000) showed that the weakly electric ¢sh Pollimyrus adspersus can distinguish interclick intervals below one millisecond. Summarizing the results from several audiological studies, Fay (1985) concluded that the auditory system of ¢shes seems particularly adapted for temporal processing but only poorly so for frequency domain processing. Therefore, we aimed to elucidate the temporal resolution abilities of several teleost species. First, we wanted to investigate species with di¡erent accessory hearing structures to determine whether the type of hearing structure in£uences temporal resolution abilities. The second goal was to examine whether the temporal resolution is su⁄cient to perceive temporal patterns of intraspeci¢c sounds. Third, we compared vocal with non-vocal species to determine whether the former exhibit better temporal resolution abilities due to their special adaptation for sound communication. We chose species having approximately the same hearing range from two taxonomic groups characterized by di¡erent accessory hearing structures: otophysans, which possess a chain of bony ossicles connecting the swim bladder to the inner ear (Weberian apparatus), and anabantoids, which have air-¢lled chambers (suprabranchial chambers or labyrinth organ) dorsal to the gills and in close contact to the saccule of the inner ear. Within each group a vocal and a non-vocal species were investigated. Within otophysines the gold¢sh Carassius auratus, a species not known to be vocal, and the Lined Raphael cat¢sh Platydoras costatus were chosen. The cat¢sh produces two types of sounds by separate sonic organs (Pfei¡er and Eisenberg, 1965; Ladich, 1997b) : low-frequency drumming sounds and broad-band stridulatory sounds, our object of interest. Among anabantoids the blue gourami Trichogaster trichopterus and the croaking gourami Trichopsis vittata were chosen. The croaking gourami produces broadband pulsed sounds by plucking enlarged pectoral ¢n tendons over bony structures (Kratochvil, 1985). As a measure of temporal resolution we recorded auditory evoked potentials in response to double-click
37
stimuli with varying click periods, a method already successfully applied to estimate the temporal resolution abilities in dolphins (Popov and Supin, 1990; Supin and Popov, 1995; Dolphin, 1997).
2. Materials and methods 2.1. Animals Test subjects were obtained from local pet suppliers except for T. vittata, which were laboratory reared. They were kept in planted aquaria whose bottoms were covered with sand, equipped with half £ower pots as hiding places, ¢ltered by external ¢lters, and maintained at a 12^12 light^dark cycle. The ¢sh were fed live Tubifex sp. or commercially prepared £ake food (Tetramin0 ) ad libitum daily. E¡orts were made to provide a quiet environment (e.g., no submerged ¢lters or air stones). Test subjects were six gold¢sh C. auratus (81^93 mm standard length (SL); 14.2^26.5 g body mass (BM)), six Lined Raphael cat¢sh P. costatus (99^107 mm SL; 22.4^26.7 g BM), seven blue gouramis T. trichopterus (47^56 mm SL; 2.7^5.0 g BM), and six croaking gouramis T. vittata (34^36 mm SL; 0.8^1.4 g BM). In addition, two specimens of the mormyrid Gnathonemus petersii (84 and 87 mm SL; 3.5 and 5.5 g BM) were measured by the same procedure in order to compare results of temporal resolution to behaviorally obtained data of a closely related mormyrid species (Marvit and Crawford, 2000). All experiments were performed with the permission of the Austrian Commission on experiments in Animals (GZ68.210/30-Pr/4/2001). 2.2. Auditory brainstem response (ABR) recordings The ABR recording protocol used in this study followed that recently described in Ladich (1999) and Wysocki and Ladich (2001). Therefore, only a brief summary of the basic technique is given here. Details on the temporal measurements will be given separately. During the experiments, the ¢sh were mildly immobilized with Flaxedil (gallamine triethiodide, Sigma). The dosage used was 0.47 Wg g31 for C. auratus, 1.33 Wg g31 for P. costatus, 0.67^1 Wg g31 for T. trichopterus, and 0.3^ 0.45 Wg g31 for T. vittata. This dosage allowed the ¢sh to retain slight opercular movements during the experiment but without signi¢cant myogenic noise to interfere with the recording. Test subjects were secured in a halfbowl-shaped plastic tub (37 cm diameter, 8 cm water depth, 2 cm layer of ¢ne sand) lined with acoustically absorbent material (closed cell foam) in order to reduce resonances and re£ections and thus to preserve the tem-
HEARES 3864 2-7-02
38
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
poral structure of the stimuli. This was con¢rmed by comparing oscillograms, power spectra and sonagrams of double-click stimuli recorded in the same tank with and without lining (Fig. 1B,C). Fish were adjusted so that the nape of the head was just above the surface of the water, and a respiration pipette was inserted into the subject’s mouth. Respiration was achieved through a simple temperature-controlled (24 N 1‡C), gravity-fed water circulation system. The ABRs were recorded using silver wire electrodes (0.25 mm diameter) pressed ¢rmly against the skin. The contacting point of both electrodes was positioned about 1 mm above the water surface. The portion of the head above the water surface was covered by a small piece of Kimwipes tissue paper to keep it moist and in order to ensure proper contact during experiments. The recording electrode was placed in the midline of the skull over the region of the medulla. The reference electrode was placed cranially between the nares. The plastic tub was positioned on an air table (TMC Micro-g 63-540) which rested on a vibration-isolated concrete plate. The entire setup was enclosed in a walk-in sound-proof room, which was constructed as a Faraday cage (interior dimensions: 3.2U3.2U2.4 m). Both sound stimuli presentation and ABR waveform recording were accomplished using a Tucker^Davis Technologies (Gainesville, FL, USA) modular rackmount system controlled by an optically linked 200 MHz MMX Pentium PC containing a TDT digital processing board and running TDT ‘Bio-Sig’ 2.2 software.
Fig. 1. (A) Averaged cepstrum-smoothed sound power spectrum of a series of double clicks with a click period of 6 ms. (B) Oscillogram of a double-click stimulus. The double-headed arrow indicates the click period measured for the control of stimulus characteristics. (C) An oscillogram of the same double-click stimulus recorded in the tank prior to lining. All stimuli were recorded under water with the hydrophone 2 cm apart from the animal.
2.3. Stimuli Sound stimuli consisted of repeated clicks and double clicks generated by TDT ‘Sig-Gen’ software, and fed through a DA1 digital-analog converter, a PA4 programmable attenuator, and a power ampli¢er (Denon PMA 715R). A dual-cone speaker (Tannoy System 600; frequency response 50 Hz^15 kHz N 3 dB), mounted 1 m above test subjects in the air, was used to present the stimuli during testing. Each type of stimulus (single clicks and click pairs) was presented to the animals at a repetition rate of 35 per second. A hydrophone (Bru«el and Kjaer 8101; frequency range : 1 Hz^80 kHz N 2 dB; voltage sensitivity: 3184 dB re 1 V/WPa) was placed close to the right side of the animals (2 cm apart) in order to control for stimulus characteristics (such as sound pressure level (SPL) and temporal structure) under water in close vicinity of the subjects (Fig. 1). For each test condition, 1000 stimuli were presented at opposite polarities and averaged by the Bio-Sig software in order to eliminate stimulus artifacts. SPLs of single-click stimuli were reduced in 4 dB steps until the ABR waveform was no longer apparent. The lowest SPL for which a repeatable ABR trace could be ob-
tained, as determined by overlaying replicate traces, was considered the threshold. This method of visual inspection correlation is the traditional means of determining thresholds in ABR audiometry (Kileny and Shea, 1986; Gorga et al., 1988; Hall, 1992) and proved also to agree well with the correlation coe⁄cient method developed by Yan (1998 ; in Scholik and Yan, 2001). Double-click stimuli were presented at three di¡erent dB levels above the hearing threshold of each particular species: 32 dB (28 dB for the anabantoids), 20 dB, and 12 dB. Fifteen di¡erent click periods were presented in di¡erent orders (starting with the shortest or the longest click period). Click periods tested were 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, and 10 ms. 2.4. ABR analysis The amplitudes of the responses to the second click of each pair of clicks were measured and compared to the response to a single click. For each species, the most constant peaks were used for analysis (Fig. 2). The ABR components were denominated with P for positive peaks (directed upwards) and N for negative peaks (di-
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
39
The pulse period of sounds was de¢ned as the time elapsed between the peak amplitudes of the two consecutive pulses within a sound and measured from oscillograms of the sounds recorded. For T. vittata, both single-pulse periods and double-pulse periods were measured (see also Fig. 8). Six to eight sounds of eight individuals were analyzed for each species.
3. Results 3.1. Characteristics of ABRs evoked by a single click
Fig. 2. Grand average ABRs of the four species investigated (Ca ^ C. auratus, Pc ^ P. costatus, Tt ^ T. trichopterus, Tv ^ T. vittata) in response to a click stimulus at 32 dB (28 dB for the anabantoids, left side) above hearing threshold including the designation of the peaks used in this study. Positive peaks (P) showing upwards, negative peaks (N) showing downwards. The double-headed arrows indicate the amplitudes measured for analysis.
rected downwards) by ascending arabic numbers. The peak-to-peak amplitudes were measured between peaks N1 and P2 for C. auratus, T. vittata and P. costatus, and between P2 and N2 for T. trichopterus. 2.5. Sound analysis Stridulatory sounds of P. costatus were recorded in the same plastic tub in which ABR measurements were conducted. Fish were held under water about 5^10 cm away from the hydrophone in the middle of the tank. Sounds were recorded on a DAT recorder (HHB, PDR 1000) using a hydrophone (Bru«el and KjVr 8101) and then analyzed using S_Tools, the Integrated Workstation for Acoustics, Speech and Signal Processing developed by the Research Laboratory of Acoustics at the Austrian Academy of Sciences. Sounds recorded in the course of a previous study (Ladich, 1998) were used to analyze the croaking sounds of T. vittata.
ABRs of all four species investigated consisted of a series of positive and negative de£ections which occurred mainly within the ¢rst 4 ms following a click stimulus and lasted each for less than 1 ms. The responses to a given stimulus were very constant between single individuals of the same species and could be averaged to form a grand average ABR waveform having the same characteristics as the individual ABRs. The main positive and negative waves of the ABRs analyzed in this study were designated for each species. Waveform shape di¡ered between species, being more similar within than between taxa (Fig. 2). ABRs of the otophysans started with a downward de£ection, whereas the ABRs of the anabantoids started with a positive peak. Individual de£ections of the latter had a shorter duration than those of the otophysans. Onset peak latencies were shorter in the anabantoids than in the otophysines (Table 1). The increase in the latencies with decreasing stimulus level was much larger in the two otophysan species. The onset latency increased by 0.39 ms for C. auratus, 0.45 ms for P. costatus, 0.03 ms for T. trichopterus, and 0.06 ms for T. vittata per 20 dB decrease in SPL in the range used for the time resolution experiments. 3.2. ABR dependence on stimulus intensity The response amplitude increased with stimulus intensity. This increase was nearly linear at high SPLs for C. auratus, P. costatus and T. trichopterus, whereas the function reached asymptotic values in T. vittata (Fig.
Table 1 Latencies for the main ABR peaks of the four species investigated
C. auratus P. costatus
T. trichopterus T. vittata
N1
N2
1.34 N 0.02 1.03 N 0.02
1.84 N 0.04
P1
P2
P3
2.11 N 0.05
2.82 N 0.03 2.67 N 0.08
3.6 N 0.06 3.49 N 0.11
P1
N1
P2
N2
P3
0.88 N 0.01 0.87 N 0.03
1.30 N 0.04 1.28 N 0.05
1.68 N 0.05 1.78 N 0.05
2.39 N 0.04 2.39 N 0.10
2.81 N 0.04 3.08 N 0.24
Auditory evoked potentials were elicited by a click stimulus at 20 dB above HL; latency values are given in ms ( N S.E.M.)
HEARES 3864 2-7-02
40
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
Fig. 3. Dependence of ABR amplitude on click SPL.
3). In all four species the slope of the function was shallower at levels around 20 dB above hearing level (HL) and lower. The shape of the ABRs remained mostly unchanged over a wide intensity range but changed at very low stimulus levels. Close to the hearing threshold, N1 and N2 as well as P1 and P2 fused so that only one negative and positive peak remained in P. costatus. P1 and P3 tended to disappear near the threshold in C. auratus (Fig. 4). In both anabantoids, P3 tended to disappear near the hearing threshold, especially in T. vittata where this peak was less pronounced than in T. trichopterus. In some cases P1 disappeared, too. 3.3. ABRs in response to double clicks Double-click stimuli evoked either one or two responses depending on the click period. At a click period of 3.5 ms, two distinct ABRs were clearly detectable in all four species (Fig. 5). At shorter click periods, however, the responses to the ¢rst and to the second click were partially superimposed. The response to the sec-
Fig. 4. ABRs of a gold¢sh recorded at di¡erent SPLs (dB re 1 WPa) with positive peaks (P1, P2, P3) designated according to their appearance.
ond click manifested itself in a changed form compared with the response to a single click (Fig. 6A). In order to isolate the response to the second click within a pair of clicks, a point-to-point subtraction procedure was performed. The response to a single click (occurring at equal time and SPL as the ¢rst click of the pair) was subtracted from the response to a double click. This procedure enabled a second response to still be detected at shorter click periods (Fig. 6B). In order to detect the presence of the remaining response to the second click, the two peaks serving for analysis were used as reference points. The shortest click period at which a second
Fig. 5. ABRs of all four species investigated (Ca ^ C. auratus, Pc ^ P. costatus, Tt ^ T. trichopterus, Tv ^ T. vittata) in response to a doubleclick stimulus of 3.5 ms click period.
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
41
Fig. 6. (A) ABRs of P. costatus in response to a double-click stimulus 32 dB above hearing threshold at di¡erent click periods (ms). (B) Responses to the second click after a point-to-point subtraction of the ABR to a single click from that to the double click. The arrows indicate the moments of stimulation. Asterisks indicate the two reference peaks for analysis.
answer was still detectable was classi¢ed as the minimum resolvable click period. Caution was taken to consider only waveforms as a second response if the two reference points could clearly be detected. Comparison of the mean minimum resolvable click periods (Table 2) showed signi¢cant species-speci¢c differences (ANOVA: F3;68 = 15.47, P 6 0.001). A Sche¡e¤ post-hoc test revealed that this signi¢cance was mainly
Table 2 The mean pulse period resolvable by the auditory system Species
n
32/28 dB
20 dB
12 dB
C. P. T. T.
6 6 7 6
1.25 N 0.11 0.52 N 0.1 0.30 N 0 1.08 N 0.24
1.33 N 0.11 0.88 N 0.12 0.40 N 0.10 0.83 N 0.07
1.40 N 0.09 1.30 N 0.11 0.82 N 0.23
auratus costatus trichopterus vittata
Pulse period values are expressed in ms ( N S.E.M.); all dB values are relative to HL of each particular species.
due to T. trichopterus being signi¢cantly di¡erent from the other three species. In addition, ABRs of two G. petersii to clicks and double clicks at 20 and 12 dB above HL were recorded and analyzed utilizing the same procedure. An answer to the second click of a pair was still detectable at click periods of 0.5 ms at 20 dB above HL. At a stimulus level of 12 dB above HL, a second answer could be detected down to a click period of 0.5 ms for individual 1 and down to 1 ms for individual 2. Amplitudes of the answer to the second click of a pair were measured for each click period in order to analyze the recovery function of the excitability. For comparative purposes, all amplitudes of the response to the second click were expressed as a percentage of the amplitude of the response to a single click. The amplitudes of the answer to the second click of a pair tended to increase with increasing click period to approach the amplitude of an answer to a single click of
HEARES 3864 2-7-02
42
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
equal intensity (Fig. 7A,B). However, more detailed analysis of this recovery process showed that this increase was irregular and di¡ered between the species. P. costatus showed the most regular recovery function. At a stimulus level of 20 dB HL a recovery of 100% was reached at a click period of 4 ms. At shorter click periods of 1.5^3.5 ms, amplitude values ranged from 70 to 90%. In C. auratus an early amplitude maximum was observed at a click period of 3.5 ms (Fig. 7A). Amplitude values were constantly above 50% at click periods above 2 ms and between 80 and 100% starting from a click period of 8 ms. Clear di¡erences were found among gouramis (Fig. 7B). In T. vittata all ABR amplitudes of the second response were s 50% at click periods of 2.5 ms and more. The amplitude approached 100% at 8 ms. In contrast, in T. trichopterus the percentage of the amplitude of the responses to the second click was above 80% at all click periods tested except for 3 ms. No increase in amplitude was observed with increasing click periods.
Fig. 8. Oscillograms of (A) stridulatory sounds of P. costatus and (B) of croaking sounds of T. vittata. PP ^ Pulse period, SP ^ singlepulse period, DP ^ double-pulse period.
3.4. Sound analysis and comparison to auditory temporal resolution 3.4.1. P. costatus The pulse periods of stridulatory sounds varied within and between individuals, with minimum pulse periods at the beginning and at the end of the sounds (Fig. 8A). Pulse periods ranged from 1.1 to 33.1 ms with a mean of 6.7 ms ( N 0.17 S.E.M.; n = 769). Most pulse periods measured were longer than the mean minimum resolvable click period at comparable SPLs, and even the minimum pulse periods of 1.1^1.3 ms (n = 3) were above the minimum resolvable click periods at 32 and 20 dB above hearing threshold (Table 2). 3.4.2. T. vittata Sounds of croaking gouramis were series of broadband double pulses with main energies above 1 kHz (Fig. 8B). Double-pulse periods ranged from 18.7 to 52.6 ms (mean 35.8 N 0.51 ms, n = 242) and single-pulse periods from 3 to 11.3 ms (mean 6 N 0.1 ms; n = 328), both depending also on the size of the animal. Doubleand single-pulse periods were longer than the minimum click periods resolvable by the auditory system (Table 2).
4. Discussion Fig. 7. Amplitude of the response to the second click of a double click as a percentage of the response to a single click of equal intensity in dependence on the click period for (A) the two otophysine species and (B) the two anabantoids at a stimulus level 20 dB above hearing threshold. Only values for click periods at which all tested individuals showed a second response are presented here.
4.1. Measurements of the temporal resolution in ¢shes utilizing the ABR recording technique The ABR recording technique has recently been in-
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
troduced to measure auditory sensitivity in ¢shes (Kenyon et al., 1998). Since then this technique has been exclusively utilized to determine hearing thresholds in ¢shes. This approach yielded invaluable results in intact individuals (Ladich and Yan, 1998; Ladich, 1999) as well as after manipulating ¢sh such as blocking the auditory periphery (Yan, 1998; Kratochvil and Ladich, 2000) or exposing ¢sh to noise (Scholik and Yan, 2001). However, this methodology can also be utilized to measure other characteristics of the auditory system besides hearing thresholds. Popov and Supin (1990) successfully applied the ABR recording technique to investigate the temporal resolution ability of the auditory system in dolphins, especially with regard to their echolocating abilities. In the present study we successfully adapted it to measure the temporal resolution in ¢shes. The approach based on the playing back of double-click stimuli and varying the click periods was also applicable to teleost ¢shes, in particular in groups possessing accessory hearing structures (hearing specialists). When presenting double-click stimuli, two ABR responses were clearly distinguished at click periods longer than 3.5 ms. Temporal resolution data gained by the ABR technique in bottlenose dolphins were similar to those obtained during behavioral tests (Au et al., 1988; Au, 1990; Dubrovskiy, 1990; Popov and Supin, 1990; Supin and Popov, 1995). These observations are supported by comparing our ABR data gained in the present study on otophysine and anabantoid ¢shes to those obtained during behavioral tests in mormyrid ¢shes. P. adspersus di¡erentiated interclick intervals of less than 1 ms (Marvit and Crawford, 2000). ABR control measurements on the mormyrid G. petersii showed minimum resolvable click periods of 0.5 ms (20 dB re HL), which are in good accordance with the behavioral data previously measured in the related genus Pollimyrus. In summary, the reliability of the ABR technique was con¢rmed by the similar response of the auditory system to double-click stimuli in two classes of vertebrates as well as because ABR data are comparable to behavioral data in both taxa. This methodological approach has several advantages. It allows rapid evaluation of the temporal resolution without lengthy training, without killing animals, and without limitations on repeated testing of subjects. 4.2. ABR waveform characteristics Since the present study intended to extend the ABR recording technique to investigate temporal auditory processing, it was important to describe and analyze ABR waveform characteristics in responses to click stimuli. This has not been done so far in ¢shes, and is a prerequisite in order to ¢nd stable reference points
43
and to standardize our analyses. Since the origin of each of the waves remains unclear in ¢shes except for rays (Corwin, 1981), it is not possible to establish a clear correspondence between ABR waves in teleosts and humans. Thus, we did not apply the most common nomenclature of human medicine (in roman numbers) but designated ABR waves by enumerating both the positive and negative peaks similar to Popov and Supin (1990). In dolphins they used ascending arabic numbers. In our study, ABRs in response to click stimuli were very constant between individuals of one species with regard to the shape and latency of the waves. We carefully limited the size range of tested ¢sh in order to avoid variations due to the size (or age) factor. A previous study on croaking gouramis (Wysocki and Ladich, 2001) demonstrated that, beyond individual variations, di¡erences in peak latencies of certain ABR waves and in overall waveform shape also occurred during ontogenetic development within the same individuals, similar to mammals and birds (e.g., Dimitrieva and Gottlieb, 1994; McFadden et al., 1996; Aitkin et al., 1997; Hill et al., 1998). An increase of ABR latency with decreasing SPL is a common phenomenon in ABR measurements and has been described for mammals (e.g., Popov and Supin, 1990; Supin and Popov, 1995) as well as for ¢shes (e.g., Kenyon et al., 1998; Kratochvil and Ladich, 2000). In our recordings the two taxonomic groups seemed to di¡er slightly: wave latency showed a greater intensity dependence in the two otophysans than in the anabantoids. Also, at comparable SPLs, the onset latency of the ABRs was shorter in the anabantoids. This may re£ect di¡erences in auditory processing due to anatomical di¡erences in the peripheral accessory hearing structures, which act as pressure-to-motion transducers. The suprabranchial chamber of the anabantoids directly contacts the saccule of the inner ear in labyrinth ¢shes, whereas in otophysans the swimbladder is connected to the inner ear by a chain of bony ossicles. A dependence of the response amplitude on the stimulus intensity is also a common phenomenon in vertebrate ABRs. This dependence was not linear for the intensity range investigated. At lower stimulus levels the slope of the function was shallower than at higher levels, where it was nearly linear. The function reached asymptotic values at high SPLs only in T. vittata. Supin and Popov (1995) found an intensity dependence of dolphin ABR amplitude until approximately 60^70 dB above HL. We therefore assume that the three other teleost species measured in our study also show an asymptotic amplitude^intensity relationship at higher stimulus levels (we did not record responses to levels above 36 dB re HL). The response to double-click stimuli di¡ered in some
HEARES 3864 2-7-02
44
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
aspects from the recovery function reported in bottlenose dolphins (Popov and Supin, 1990; Supin and Popov, 1995). Whereas the response amplitude to the second click increased steadily with longer interclick intervals in Tursiops truncatus, the response amplitude of the investigated ¢shes showed an irregular increase. This perhaps re£ects di¡erences in auditory processing mechanisms of the nervous system in ¢shes and dolphins, which are particularly specialized to precisely detect consecutive clicks during echolocation. 4.3. Temporal resolution ability of ¢shes Di¡erences in minimum resolvable click periods were observed between species, but no clear trend was found between taxa or vocal species. Whereas in otophysans the vocal cat¢sh showed shorter minimum resolvable click periods, the opposite was true in anabantoids. The temporal resolution ability of these species as revealed by double-click experiments was between 0.3 and 1.4 ms and thus on the average slightly lower than that estimated for dolphins by the same technique (about 0.2^0.3 ms, Supin and Popov, 1995) ; it is, however, within the range of other vertebrate species, where it has been reported to be in the order of several milliseconds (for a review see Fay, 1988). Several authors have stressed the importance of investigating whether the auditory system of ¢shes is capable of resolving the individual pulses within pulsed sounds. This requires in several species a relatively high temporal resolution ability if they do not rely on a general ‘impression’ of sound (Popper, 1972; Hawkins, 1981; Hawkins and Myrberg, 1983). Based on various audiological studies it was assumed that the auditory system of the gold¢sh is particularly well adapted for temporal processing of acoustic stimuli compared to the frequency domain (Fay, 1982). Fishes seem to be able to detect each pulse within a sound, but only few data are available to support these assumptions (Popper, 1972). Temporal resolution has been studied using several di¡erent paradigms, each leading to di¡erent results: Based upon gap detection experiments in ongoing noise, a minimum integration time of about 35 ms was estimated for the gold¢sh (Fay and Coombs, 1984), a value considerably larger than in mammals and birds (2^4 ms; see Fay, 1985). On the other hand, behavioral and neural temporal modulation transfer functions for noise and tones based on sinusoidal amplitude modulations suggested an integration time of less than 0.4 ms in the gold¢sh (Fay, 1980). In another study, Fay et al. (1983) revealed that gold¢sh are able to detect changes of about 6^7% at echo delays in noise between 1.25 and 10 ms. For this detection of echo delays they suggested a limitation of about 1 ms due to the refractory period of saccular units. These data are comparable to the
minimum resolvable pulse period of about 1.25 ms we found in gold¢sh. The latter type of stimulation (repeated noise with delay in the onset) may also approximate our double-click stimuli paradigm. Our stimulus, consisting of short, broad-band pulses with a fast rise time, might not be suitable to investigate temporal resolution of the auditory system in hearing generalists because their narrower hearing band width would probably not yield fast rises in the stimulus waveform as does the wider band width of hearing specialists. Our knowledge of the temporal resolution in other ¢sh species and taxa is poor, especially in vocal ones where acoustic signals are important for communication. Besides the above-mentioned data from the mormyrid Pollimyrus, there is only evidence from behavioral discrimination tasks that damsel¢sh of the genus Pomacentrus must be capable of distinguishing temporal di¡erences of sounds between at least 5 and 10 ms (Myrberg et al., 1978). Altogether, teleost ¢shes seem to have temporal resolution abilities in the order of a few milliseconds or even less, which is not fundamentally di¡erent from other vertebrates such as mammals and birds. 4.4. Comparison between the temporal resolution and temporal structure of sounds The sound analysis of the two vocalizing species showed that pulse periods varied especially in P. costatus. Comparing pulse intervals of conspeci¢c sounds to the minimum resolvable click period, the auditory system of T. vittata clearly processes each of the pulses within conspeci¢c sounds separately. Naturally occurring sounds have SPLs which are within the range tested or higher. Even considering that the time resolution capability decreases with increasing SPL, it is very likely that double pulses and single pulses can be detected. The pulse periods of P. costatus’ stridulatory sounds are quite variable. Most values indicate that pulses within a sound can be processed separately by the auditory system of this cat¢sh species. Our analysis of over 700 pulses revealed that only three values (in merely one individual out of eight) were below the minimum click period resolvable at low SPLs. Therefore, we compared the levels used in this study with SPL measurements of stridulatory sounds of P. costatus in a previous study (Ladich, 1999). Those levels were up to 15 dB higher than our maximum level tested. Because in this species the minimum resolvable click period decreased with increasing dB level re HL, the auditory system of the ¢sh can probably process almost all pulses within a sound, especially because ABR waves only re£ect the ¢rst steps of auditory processing in the
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
brainstem up to the midbrain (Corwin, 1981), and ‘higher’ levels of the central nervous system might improve temporal resolution. Grunts of the mormyrids Pollimyrus isidori and P. adspersii mainly di¡er in their interclick interval, whereas another type of sound they produce di¡ers primarily in its dominant frequency. Both sounds play a role in the mating system of the ¢sh. Marvit and Crawford (2000) concluded from behavioral audiological experiments that discrimination thresholds in the mormyrids are su⁄cient to mediate species and maybe individual recognition as well. Behavioral tests in damsel¢sh (Myrberg et al., 1978) showed that their ability to discriminate acoustically between closely related sympatric species relied primarily on the pulse period of the sounds. Summarizing the sparse available data on auditory temporal resolution, the auditory capabilities of teleost ¢shes (at least of hearing specialists) are probably su⁄cient to process pulses within sounds separately. Temporal patterns of sounds can thus provide reliable information during acoustic communication. These data are in agreement with behavioral observations and the structure of many ¢sh sounds. Furthermore, these capabilities do not represent a special adaptation to intraspeci¢c communication because they are also observed in non-vocal species. Rather, these abilities rely on the properties of the auditory system and on the temporal processing by the nervous system.
Acknowledgements We would like to thank Brigitte WeiM for assistance during this study and two anonymous reviewers for critically reading the manuscript. This study was supported by the Austrian Science Fund (FWF Grant No. 12411 to F.L.).
References Aitkin, L., Cochran, S., Frost, S., Martsi-McClintock, A., Masterton, B., 1997. Features of the auditory development of the short-tailed Brazilian opossum, Monodelphis domestica: evoked responses, neonatal vocalizations and synapses in the inferior colliculus. Hear. Res. 113, 69^75. Au, W.W.L., 1990. Target detection in noise by echolocating dolphins. In: Thomas, R.A., Kastelein, R.A. (Eds.), Sensory Abilities of Cetaceans. Laboratory and Field Evidence. Plenum Press, New York, pp. 203^216. Au, W.W.L., Moore, P.W.B., Pawloski, D.A., 1988. Detection of complex echos in noise by an echolocating dolphin. J. Acoust. Soc. Am. 83, 662^668. Corwin, J.T., 1981. Audition in elasmobranchs. In: Tavolga, W.N., Popper, A.N., Fay, R.R. (Eds.), Hearing and Sound Communication in Fishes. Springer, New York, pp. 81^102.
45
Crawford, J.D., 1997. Hearing and acoustic communication in mormyrid electric ¢shes. Mar. Freshw. Behav. Physiol. 29, 65^86. Dimitrieva, L.P., Gottlieb, G., 1994. In£uence of auditory experience on the development of brain stem auditory-evoked potentials in mallard duck embryos and hatchlings. Behav. Neurol. Biol. 61, 19^28. Dolphin, W.F., 1997. Electrophysiological measures of auditory processing in odontocetes. Bioacoustics 8, 79^101. Dubrovskiy, N.A., 1990. On the two auditory systems of dolphins. In: Thomas, R.A., Kastelein, R.A. (Eds.), Sensory Abilities of Cetaceans. Laboratory and Field Evidence. Plenum Press, New York, pp. 233^254. Fay, R.R., 1980. Psychophysics and neurophysiology of temporal factors in hearing by the gold¢sh: Amplitude modulation detection. J. Neurophysiol. 44, 312^332. Fay, R.R., 1982. Neural mechanisms of an auditory temporal discrimination by the gold¢sh. J. Comp. Physiol. A 147, 201^216. Fay, R.R., 1985. Temporal processing by the auditory system of ¢shes. In: Michelsen, A. (Ed.), Time Resolution in Auditory Systems. Springer, Berlin, pp. 28^57. Fay, R.R., 1988. Hearing in Vertebrates: A Psychophysics Databook. Hill-Fay Associates, Winnetka, IL. Fay, R.R., Coombs, S.L., 1984. Sound intensity processing by the gold¢sh auditory system. J. Acoust. Soc. Am. 76, S12. Fay, R.R., Yost, W.A., Coombs, S.L., 1983. Psychophysics and neurophysiology of repetition noise processing in a vertebrate auditory system. Hear. Res. 12, 31^55. Gerald, J.W., 1971. Sound production in six species of sun¢sh (Centrarchidae). Evolution 25, 75^87. Gorga, M.P., Kaminski, L.R., Beauchaine, K.A., Jestaedt, W., 1988. Auditory brainstem response to tone bursts in normally hearing subjects. J. Speech Hear. Res. 31, 87^97. Hall, J.W., 1992. Handbook of Auditory Evoked Responses. Allyn and Bacon, Boston, MA. Hawkins, A.D., 1981. The hearing abilities of ¢sh. In: Tavolga, W.N., Popper, A.N., Fay, R.R (Eds.), Hearing and Sound Communication in Fishes. Springer, New York, pp. 109^133. Hawkins, A.D., Rasmussen, K.J., 1978. The calls of Gadoid ¢sh. J. Mar. Biol. Assoc. UK 58, 891^911. Hawkins, A.D., Myrberg, A.A., Jr., 1983. Hearing and sound communication under water. In: Lewis, B. (Ed.), Bioacoustics, a Comparative Approach. Academic Press, London, pp. 347^405. Hill, K.G., Cone-Wesson, B., Liu, G.B., 1998. Development of auditory function in the tammar wallaby Macropus eugenii. Hear. Res. 117, 97^106. Kenyon, T.N., Ladich, F., Yan, H.Y., 1998. A comparative study of hearing ability in ¢shes: the auditory brainstem response approach. J. Comp. Physiol. A 182, 307^318. Kileny, P., Shea, S.L., 1986. Middle-latency and 40-Hz auditory evoked responses in normal-hearing subjects: clicks and 500 Hz thresholds. J. Speech Hear. Res. 29, 20^28. Kratochvil, H., 1985. Beitra«ge zur Lautbiologie der Anabantoidei ^ Bau, Funktion und Entwicklung von lauterzeugenden Systemen. Zool. Jahrb. Physiol. 89, 203^255. Kratochvil, H., Ladich, F., 2000. Auditory role of lateral trunk channels in cobitid ¢shes. J. Comp. Physiol. A 186, 279^285. Ladich, F., 1997a. Agonistic behavior and signi¢cance of sounds in vocalizing ¢sh. Mar. Freshw. Behav. Physiol. 29, 87^108. Ladich, F., 1997b. Comparative analysis of swimbladder (drumming) and pectoral (stridulation) sounds in three families of cat¢shes. Bioacoustics 8, 85^208. Ladich, F., 1998. Sound characteristics and outcome of contests in male croaking gouramis (Teleostei). Ethology 104, 517^529. Ladich, F., 1999. Did auditory sensitivity and vocalization evolve independently in otophysan ¢shes? Brain Behav. Evol. 53, 288^304.
HEARES 3864 2-7-02
46
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
Ladich, F., Yan, H.Y., 1998. Correlation between auditory sensitivity and vocalization in anabantoid ¢shes. J. Comp. Physiol. A 182, 737^746. Ladich, F., Bischof, C., Schleinzer, G., Fuchs, A., 1992. Intra- and interspeci¢c di¡erences in agonistic vocalization in croaking gouramis (genus: Trichopsis, Anabantoidei, Teleostei). Bioacoustics 4, 131^141. Mann, D.A., Lobel, P.S., 1997. Propagation of damsel¢sh (Pomacentridae) courtship sounds. J. Acoust. Soc. Am. 101, 3783^3791. Marvit, P., Crawford, J.D., 2000. Auditory discrimination in a soundproducing electric ¢sh (Pollimyrus): tone frequency and click-rate di¡erence detection. J. Acoust. Soc. Am. 108, 1819^1825. McFadden, S.L., Walsh, E.J., McGee, J., 1996. Onset and development of auditory brainstem response in the Mongolian Gerbil (Meriones unguiculatus). Hear. Res. 100, 68^79. McKibben, J.R., Bass, A.H., 1998. Behavioral assessment of acoustic parameters relevant to signal recognition and preference in a vocal ¢sh. J. Acoust. Soc. Am. 104, 3520^3533. Myrberg, A.A., Jr., Spires, J.Y., 1972. Sound discrimination by the bicolor damsel¢sh, Eupomacentrus partitus. J. Exp. Biol. 57, 727^735. Myrberg, A.A., Jr., Spanier, E., Ha, S.J., 1978. Temporal patterning in acoustic communication. In: Reese, E.S., Lighter, F.J. (Eds.), Contrasts in Behaviour. John Wiley and Sons, New York, pp. 137^179. Myrberg, A.A., Jr., Mohler, M., Catala, J.D., 1986. Sound production by males of a coral reef ¢sh (Pomacentrus partitus): its signi¢cance to females. Anim. Behav. 34, 913^923. Pfei¡er, W., Eisenberg, J.F., 1965. Die Lauterzeugung der Dornwelse
(Doradidae) und der Fiederbartwelse (Mochokidae). Z. Morph. º kol. Tiere 54, 669^679. O Popov, V.V., Supin, A.Y., 1990. Auditory brain stem responses in characterization of dolphin hearing. J. Comp. Physiol. A 166, 385^393. Popper, A.N., 1972. Auditory threshold in the gold¢sh (Carassius auratus) as a function of signal duration. J. Acoust. Soc. Am. 52, 596^602. Pruzsinszky, I., Ladich, F., 1998. Sound production and reproductive behaviour of the armoured cat¢sh Corydoras paleatus (Callichthyidae). Environ. Biol. Fish. 53, 183^191. Scholik, A.R., Yan, H.Y., 2001. E¡ects of underwater noise on auditory sensitivity of a cyprinid ¢sh. Hear. Res. 152, 17^24. Supin, A.Y., Popov, V.V., 1995. Temporal resolution in the dolphin’s auditory system revealed by double-click evoked potential study. J. Acoust. Soc. Am. 97, 2586^2593. Winn, H.E., 1964. The biological signi¢cance of ¢sh sounds. In: Tavolga, W.N. (Ed.), Marine Bioacoustics, Vol. 2. Pergamon Press, New York, pp. 213^231. Winn, H.E., 1967. Vocal facilitation and the biological signi¢cance of toad¢sh sounds. In: Tavolga, W.N. (Ed.), Marine Bioacoustics, Vol. 2. Pergamon Press, New York, pp. 283^303. Wysocki, L.E., Ladich, F., 2001. The ontogenetic development of auditory sensitivity, vocalization and acoustic communication in the labyrinth ¢sh Trichopsis vittata. J. Comp. Physiol. A 187, 177^ 187. Yan, H.Y., 1998. Auditory role of the suprabranchial chamber in gourami ¢sh. J. Comp. Physiol. A 183, 325^333.
HEARES 3864 2-7-02
Can ¢shes resolve temporal characteristics of sounds? New insights using auditory brainstem responses Lidia Eva Wysocki , Friedrich Ladich Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria Received 14 November 2001; accepted 31 January 2002
Abstract Numerous fish species produce broad-band pulsed sounds with a distinct temporal patterning which is thought to be important during intraspecific communication. In order to determine whether fishes are able to utilize temporal characteristics of acoustic signals, time resolution was determined in four species of otophysines and anabantoids by analyzing auditory brainstem responses (ABRs) to double-click stimuli with varying click periods. At click periods of 3.5 ms, two distinct ABRs were clearly detectable in all species. The minimum pulse period resolvable by the auditory system was below 1.5 ms in each species and slightly intensitydependent. No differences were found between vocal and non-vocal species within each taxon. Comparisons of the time resolution data to the pulse periods of intraspecific sounds in the vocal species showed that the otophysine Platydoras costatus and the anabantoid Trichopsis vittata are likely to process each pulse within a series of intraspecific sounds. However, as non-vocal and vocal species have a similar minimum resolvable click period, the high temporal resolution capacities of the auditory system of fish might not represent special adaptations for intraspecific acoustic communication. Nonetheless, we suggest that temporal characteristics of naturally occurring conspecific and heterospecific sounds provide reliable information for acoustic communication. 4 2002 Elsevier Science B.V. All rights reserved. Key words: Auditory temporal resolution; Auditory brainstem response; Teleost ; Temporal sound pattern; Acoustic communication
1. Introduction Sound production is widespread among ¢shes and occurs in various contexts such as in distress situations or during social interactions. Acoustic signals play a role in the mating systems of several groups such as damsel¢shes (Myrberg et al., 1986), sun¢shes (Gerald, 1971), toad¢shes (McKibben and Bass, 1998), mormyrids (Crawford, 1997), and cat¢sh (Pruzsinszky and Ladich, 1998) as well as during agonistic interactions (for a review see Ladich, 1997a). Information transmitted by
* Corresponding author. Tel.: +431 4277 54515; Fax: +431 4277 9544. E-mail address: [email protected] (L.E. Wysocki). Abbreviations: ABR, auditory brainstem response; BM, body mass; HL, hearing level; SL, standard length; SPL, sound pressure level
acoustic signals could be encoded by their frequency, intensity, or temporal content. Fish sounds often consist of series of short broadband pulses (e.g., stridulatory sounds of gouramis and cat¢shes; Ladich et al., 1992; Ladich, 1997b) with distinct temporal patterns, whereby interpulse intervals vary from only a few up to several dozen milliseconds (Myrberg et al., 1978; Ladich et al., 1992; Pruzsinszky and Ladich, 1998). Therefore, several researchers have suggested that ¢sh sounds code information in the time rather than frequency domain (Winn, 1964, 1967; Myrberg et al., 1978). Winn (1964) demonstrated that temporal properties of sounds such as unit duration and repetition rate play a decisive role in the communication system of the oyster toad¢sh Opsanus tau. Courtship sounds in closely related species of sun¢shes (Gerald, 1971), pomacentrids (Myrberg et al., 1986), mormyrids (Marvit and Crawford, 2000), as well as calls of various vocal gadoid ¢sh mainly di¡er in their
0378-5955 / 02 / $ ^ see front matter 4 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 5 9 5 5 ( 0 2 ) 0 0 3 3 6 - 2
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
temporal patterning (Hawkins and Rasmussen, 1978). In the haddock Melanogrammus aegle¢nus, the distinct sounds produced in various contexts di¡er in terms of their structure in the time domain. Temporal patterns of sounds, namely the pulse period, proved to be the most important factor for species recognition in damsel¢shes (Myrberg and Spires, 1972). Furthermore, Mann and Lobel (1997) demonstrated that during sound propagation the most reliable information is transferred by the pulse period of damsel¢sh sounds. Considering the assumed importance of temporal patterns in sound communication, surprisingly little is known about the temporal resolution abilities of the auditory system of ¢shes. A recent study (Marvit and Crawford, 2000) showed that the weakly electric ¢sh Pollimyrus adspersus can distinguish interclick intervals below one millisecond. Summarizing the results from several audiological studies, Fay (1985) concluded that the auditory system of ¢shes seems particularly adapted for temporal processing but only poorly so for frequency domain processing. Therefore, we aimed to elucidate the temporal resolution abilities of several teleost species. First, we wanted to investigate species with di¡erent accessory hearing structures to determine whether the type of hearing structure in£uences temporal resolution abilities. The second goal was to examine whether the temporal resolution is su⁄cient to perceive temporal patterns of intraspeci¢c sounds. Third, we compared vocal with non-vocal species to determine whether the former exhibit better temporal resolution abilities due to their special adaptation for sound communication. We chose species having approximately the same hearing range from two taxonomic groups characterized by di¡erent accessory hearing structures: otophysans, which possess a chain of bony ossicles connecting the swim bladder to the inner ear (Weberian apparatus), and anabantoids, which have air-¢lled chambers (suprabranchial chambers or labyrinth organ) dorsal to the gills and in close contact to the saccule of the inner ear. Within each group a vocal and a non-vocal species were investigated. Within otophysines the gold¢sh Carassius auratus, a species not known to be vocal, and the Lined Raphael cat¢sh Platydoras costatus were chosen. The cat¢sh produces two types of sounds by separate sonic organs (Pfei¡er and Eisenberg, 1965; Ladich, 1997b) : low-frequency drumming sounds and broad-band stridulatory sounds, our object of interest. Among anabantoids the blue gourami Trichogaster trichopterus and the croaking gourami Trichopsis vittata were chosen. The croaking gourami produces broadband pulsed sounds by plucking enlarged pectoral ¢n tendons over bony structures (Kratochvil, 1985). As a measure of temporal resolution we recorded auditory evoked potentials in response to double-click
37
stimuli with varying click periods, a method already successfully applied to estimate the temporal resolution abilities in dolphins (Popov and Supin, 1990; Supin and Popov, 1995; Dolphin, 1997).
2. Materials and methods 2.1. Animals Test subjects were obtained from local pet suppliers except for T. vittata, which were laboratory reared. They were kept in planted aquaria whose bottoms were covered with sand, equipped with half £ower pots as hiding places, ¢ltered by external ¢lters, and maintained at a 12^12 light^dark cycle. The ¢sh were fed live Tubifex sp. or commercially prepared £ake food (Tetramin0 ) ad libitum daily. E¡orts were made to provide a quiet environment (e.g., no submerged ¢lters or air stones). Test subjects were six gold¢sh C. auratus (81^93 mm standard length (SL); 14.2^26.5 g body mass (BM)), six Lined Raphael cat¢sh P. costatus (99^107 mm SL; 22.4^26.7 g BM), seven blue gouramis T. trichopterus (47^56 mm SL; 2.7^5.0 g BM), and six croaking gouramis T. vittata (34^36 mm SL; 0.8^1.4 g BM). In addition, two specimens of the mormyrid Gnathonemus petersii (84 and 87 mm SL; 3.5 and 5.5 g BM) were measured by the same procedure in order to compare results of temporal resolution to behaviorally obtained data of a closely related mormyrid species (Marvit and Crawford, 2000). All experiments were performed with the permission of the Austrian Commission on experiments in Animals (GZ68.210/30-Pr/4/2001). 2.2. Auditory brainstem response (ABR) recordings The ABR recording protocol used in this study followed that recently described in Ladich (1999) and Wysocki and Ladich (2001). Therefore, only a brief summary of the basic technique is given here. Details on the temporal measurements will be given separately. During the experiments, the ¢sh were mildly immobilized with Flaxedil (gallamine triethiodide, Sigma). The dosage used was 0.47 Wg g31 for C. auratus, 1.33 Wg g31 for P. costatus, 0.67^1 Wg g31 for T. trichopterus, and 0.3^ 0.45 Wg g31 for T. vittata. This dosage allowed the ¢sh to retain slight opercular movements during the experiment but without signi¢cant myogenic noise to interfere with the recording. Test subjects were secured in a halfbowl-shaped plastic tub (37 cm diameter, 8 cm water depth, 2 cm layer of ¢ne sand) lined with acoustically absorbent material (closed cell foam) in order to reduce resonances and re£ections and thus to preserve the tem-
HEARES 3864 2-7-02
38
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
poral structure of the stimuli. This was con¢rmed by comparing oscillograms, power spectra and sonagrams of double-click stimuli recorded in the same tank with and without lining (Fig. 1B,C). Fish were adjusted so that the nape of the head was just above the surface of the water, and a respiration pipette was inserted into the subject’s mouth. Respiration was achieved through a simple temperature-controlled (24 N 1‡C), gravity-fed water circulation system. The ABRs were recorded using silver wire electrodes (0.25 mm diameter) pressed ¢rmly against the skin. The contacting point of both electrodes was positioned about 1 mm above the water surface. The portion of the head above the water surface was covered by a small piece of Kimwipes tissue paper to keep it moist and in order to ensure proper contact during experiments. The recording electrode was placed in the midline of the skull over the region of the medulla. The reference electrode was placed cranially between the nares. The plastic tub was positioned on an air table (TMC Micro-g 63-540) which rested on a vibration-isolated concrete plate. The entire setup was enclosed in a walk-in sound-proof room, which was constructed as a Faraday cage (interior dimensions: 3.2U3.2U2.4 m). Both sound stimuli presentation and ABR waveform recording were accomplished using a Tucker^Davis Technologies (Gainesville, FL, USA) modular rackmount system controlled by an optically linked 200 MHz MMX Pentium PC containing a TDT digital processing board and running TDT ‘Bio-Sig’ 2.2 software.
Fig. 1. (A) Averaged cepstrum-smoothed sound power spectrum of a series of double clicks with a click period of 6 ms. (B) Oscillogram of a double-click stimulus. The double-headed arrow indicates the click period measured for the control of stimulus characteristics. (C) An oscillogram of the same double-click stimulus recorded in the tank prior to lining. All stimuli were recorded under water with the hydrophone 2 cm apart from the animal.
2.3. Stimuli Sound stimuli consisted of repeated clicks and double clicks generated by TDT ‘Sig-Gen’ software, and fed through a DA1 digital-analog converter, a PA4 programmable attenuator, and a power ampli¢er (Denon PMA 715R). A dual-cone speaker (Tannoy System 600; frequency response 50 Hz^15 kHz N 3 dB), mounted 1 m above test subjects in the air, was used to present the stimuli during testing. Each type of stimulus (single clicks and click pairs) was presented to the animals at a repetition rate of 35 per second. A hydrophone (Bru«el and Kjaer 8101; frequency range : 1 Hz^80 kHz N 2 dB; voltage sensitivity: 3184 dB re 1 V/WPa) was placed close to the right side of the animals (2 cm apart) in order to control for stimulus characteristics (such as sound pressure level (SPL) and temporal structure) under water in close vicinity of the subjects (Fig. 1). For each test condition, 1000 stimuli were presented at opposite polarities and averaged by the Bio-Sig software in order to eliminate stimulus artifacts. SPLs of single-click stimuli were reduced in 4 dB steps until the ABR waveform was no longer apparent. The lowest SPL for which a repeatable ABR trace could be ob-
tained, as determined by overlaying replicate traces, was considered the threshold. This method of visual inspection correlation is the traditional means of determining thresholds in ABR audiometry (Kileny and Shea, 1986; Gorga et al., 1988; Hall, 1992) and proved also to agree well with the correlation coe⁄cient method developed by Yan (1998 ; in Scholik and Yan, 2001). Double-click stimuli were presented at three di¡erent dB levels above the hearing threshold of each particular species: 32 dB (28 dB for the anabantoids), 20 dB, and 12 dB. Fifteen di¡erent click periods were presented in di¡erent orders (starting with the shortest or the longest click period). Click periods tested were 0.3, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, and 10 ms. 2.4. ABR analysis The amplitudes of the responses to the second click of each pair of clicks were measured and compared to the response to a single click. For each species, the most constant peaks were used for analysis (Fig. 2). The ABR components were denominated with P for positive peaks (directed upwards) and N for negative peaks (di-
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
39
The pulse period of sounds was de¢ned as the time elapsed between the peak amplitudes of the two consecutive pulses within a sound and measured from oscillograms of the sounds recorded. For T. vittata, both single-pulse periods and double-pulse periods were measured (see also Fig. 8). Six to eight sounds of eight individuals were analyzed for each species.
3. Results 3.1. Characteristics of ABRs evoked by a single click
Fig. 2. Grand average ABRs of the four species investigated (Ca ^ C. auratus, Pc ^ P. costatus, Tt ^ T. trichopterus, Tv ^ T. vittata) in response to a click stimulus at 32 dB (28 dB for the anabantoids, left side) above hearing threshold including the designation of the peaks used in this study. Positive peaks (P) showing upwards, negative peaks (N) showing downwards. The double-headed arrows indicate the amplitudes measured for analysis.
rected downwards) by ascending arabic numbers. The peak-to-peak amplitudes were measured between peaks N1 and P2 for C. auratus, T. vittata and P. costatus, and between P2 and N2 for T. trichopterus. 2.5. Sound analysis Stridulatory sounds of P. costatus were recorded in the same plastic tub in which ABR measurements were conducted. Fish were held under water about 5^10 cm away from the hydrophone in the middle of the tank. Sounds were recorded on a DAT recorder (HHB, PDR 1000) using a hydrophone (Bru«el and KjVr 8101) and then analyzed using S_Tools, the Integrated Workstation for Acoustics, Speech and Signal Processing developed by the Research Laboratory of Acoustics at the Austrian Academy of Sciences. Sounds recorded in the course of a previous study (Ladich, 1998) were used to analyze the croaking sounds of T. vittata.
ABRs of all four species investigated consisted of a series of positive and negative de£ections which occurred mainly within the ¢rst 4 ms following a click stimulus and lasted each for less than 1 ms. The responses to a given stimulus were very constant between single individuals of the same species and could be averaged to form a grand average ABR waveform having the same characteristics as the individual ABRs. The main positive and negative waves of the ABRs analyzed in this study were designated for each species. Waveform shape di¡ered between species, being more similar within than between taxa (Fig. 2). ABRs of the otophysans started with a downward de£ection, whereas the ABRs of the anabantoids started with a positive peak. Individual de£ections of the latter had a shorter duration than those of the otophysans. Onset peak latencies were shorter in the anabantoids than in the otophysines (Table 1). The increase in the latencies with decreasing stimulus level was much larger in the two otophysan species. The onset latency increased by 0.39 ms for C. auratus, 0.45 ms for P. costatus, 0.03 ms for T. trichopterus, and 0.06 ms for T. vittata per 20 dB decrease in SPL in the range used for the time resolution experiments. 3.2. ABR dependence on stimulus intensity The response amplitude increased with stimulus intensity. This increase was nearly linear at high SPLs for C. auratus, P. costatus and T. trichopterus, whereas the function reached asymptotic values in T. vittata (Fig.
Table 1 Latencies for the main ABR peaks of the four species investigated
C. auratus P. costatus
T. trichopterus T. vittata
N1
N2
1.34 N 0.02 1.03 N 0.02
1.84 N 0.04
P1
P2
P3
2.11 N 0.05
2.82 N 0.03 2.67 N 0.08
3.6 N 0.06 3.49 N 0.11
P1
N1
P2
N2
P3
0.88 N 0.01 0.87 N 0.03
1.30 N 0.04 1.28 N 0.05
1.68 N 0.05 1.78 N 0.05
2.39 N 0.04 2.39 N 0.10
2.81 N 0.04 3.08 N 0.24
Auditory evoked potentials were elicited by a click stimulus at 20 dB above HL; latency values are given in ms ( N S.E.M.)
HEARES 3864 2-7-02
40
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
Fig. 3. Dependence of ABR amplitude on click SPL.
3). In all four species the slope of the function was shallower at levels around 20 dB above hearing level (HL) and lower. The shape of the ABRs remained mostly unchanged over a wide intensity range but changed at very low stimulus levels. Close to the hearing threshold, N1 and N2 as well as P1 and P2 fused so that only one negative and positive peak remained in P. costatus. P1 and P3 tended to disappear near the threshold in C. auratus (Fig. 4). In both anabantoids, P3 tended to disappear near the hearing threshold, especially in T. vittata where this peak was less pronounced than in T. trichopterus. In some cases P1 disappeared, too. 3.3. ABRs in response to double clicks Double-click stimuli evoked either one or two responses depending on the click period. At a click period of 3.5 ms, two distinct ABRs were clearly detectable in all four species (Fig. 5). At shorter click periods, however, the responses to the ¢rst and to the second click were partially superimposed. The response to the sec-
Fig. 4. ABRs of a gold¢sh recorded at di¡erent SPLs (dB re 1 WPa) with positive peaks (P1, P2, P3) designated according to their appearance.
ond click manifested itself in a changed form compared with the response to a single click (Fig. 6A). In order to isolate the response to the second click within a pair of clicks, a point-to-point subtraction procedure was performed. The response to a single click (occurring at equal time and SPL as the ¢rst click of the pair) was subtracted from the response to a double click. This procedure enabled a second response to still be detected at shorter click periods (Fig. 6B). In order to detect the presence of the remaining response to the second click, the two peaks serving for analysis were used as reference points. The shortest click period at which a second
Fig. 5. ABRs of all four species investigated (Ca ^ C. auratus, Pc ^ P. costatus, Tt ^ T. trichopterus, Tv ^ T. vittata) in response to a doubleclick stimulus of 3.5 ms click period.
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
41
Fig. 6. (A) ABRs of P. costatus in response to a double-click stimulus 32 dB above hearing threshold at di¡erent click periods (ms). (B) Responses to the second click after a point-to-point subtraction of the ABR to a single click from that to the double click. The arrows indicate the moments of stimulation. Asterisks indicate the two reference peaks for analysis.
answer was still detectable was classi¢ed as the minimum resolvable click period. Caution was taken to consider only waveforms as a second response if the two reference points could clearly be detected. Comparison of the mean minimum resolvable click periods (Table 2) showed signi¢cant species-speci¢c differences (ANOVA: F3;68 = 15.47, P 6 0.001). A Sche¡e¤ post-hoc test revealed that this signi¢cance was mainly
Table 2 The mean pulse period resolvable by the auditory system Species
n
32/28 dB
20 dB
12 dB
C. P. T. T.
6 6 7 6
1.25 N 0.11 0.52 N 0.1 0.30 N 0 1.08 N 0.24
1.33 N 0.11 0.88 N 0.12 0.40 N 0.10 0.83 N 0.07
1.40 N 0.09 1.30 N 0.11 0.82 N 0.23
auratus costatus trichopterus vittata
Pulse period values are expressed in ms ( N S.E.M.); all dB values are relative to HL of each particular species.
due to T. trichopterus being signi¢cantly di¡erent from the other three species. In addition, ABRs of two G. petersii to clicks and double clicks at 20 and 12 dB above HL were recorded and analyzed utilizing the same procedure. An answer to the second click of a pair was still detectable at click periods of 0.5 ms at 20 dB above HL. At a stimulus level of 12 dB above HL, a second answer could be detected down to a click period of 0.5 ms for individual 1 and down to 1 ms for individual 2. Amplitudes of the answer to the second click of a pair were measured for each click period in order to analyze the recovery function of the excitability. For comparative purposes, all amplitudes of the response to the second click were expressed as a percentage of the amplitude of the response to a single click. The amplitudes of the answer to the second click of a pair tended to increase with increasing click period to approach the amplitude of an answer to a single click of
HEARES 3864 2-7-02
42
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
equal intensity (Fig. 7A,B). However, more detailed analysis of this recovery process showed that this increase was irregular and di¡ered between the species. P. costatus showed the most regular recovery function. At a stimulus level of 20 dB HL a recovery of 100% was reached at a click period of 4 ms. At shorter click periods of 1.5^3.5 ms, amplitude values ranged from 70 to 90%. In C. auratus an early amplitude maximum was observed at a click period of 3.5 ms (Fig. 7A). Amplitude values were constantly above 50% at click periods above 2 ms and between 80 and 100% starting from a click period of 8 ms. Clear di¡erences were found among gouramis (Fig. 7B). In T. vittata all ABR amplitudes of the second response were s 50% at click periods of 2.5 ms and more. The amplitude approached 100% at 8 ms. In contrast, in T. trichopterus the percentage of the amplitude of the responses to the second click was above 80% at all click periods tested except for 3 ms. No increase in amplitude was observed with increasing click periods.
Fig. 8. Oscillograms of (A) stridulatory sounds of P. costatus and (B) of croaking sounds of T. vittata. PP ^ Pulse period, SP ^ singlepulse period, DP ^ double-pulse period.
3.4. Sound analysis and comparison to auditory temporal resolution 3.4.1. P. costatus The pulse periods of stridulatory sounds varied within and between individuals, with minimum pulse periods at the beginning and at the end of the sounds (Fig. 8A). Pulse periods ranged from 1.1 to 33.1 ms with a mean of 6.7 ms ( N 0.17 S.E.M.; n = 769). Most pulse periods measured were longer than the mean minimum resolvable click period at comparable SPLs, and even the minimum pulse periods of 1.1^1.3 ms (n = 3) were above the minimum resolvable click periods at 32 and 20 dB above hearing threshold (Table 2). 3.4.2. T. vittata Sounds of croaking gouramis were series of broadband double pulses with main energies above 1 kHz (Fig. 8B). Double-pulse periods ranged from 18.7 to 52.6 ms (mean 35.8 N 0.51 ms, n = 242) and single-pulse periods from 3 to 11.3 ms (mean 6 N 0.1 ms; n = 328), both depending also on the size of the animal. Doubleand single-pulse periods were longer than the minimum click periods resolvable by the auditory system (Table 2).
4. Discussion Fig. 7. Amplitude of the response to the second click of a double click as a percentage of the response to a single click of equal intensity in dependence on the click period for (A) the two otophysine species and (B) the two anabantoids at a stimulus level 20 dB above hearing threshold. Only values for click periods at which all tested individuals showed a second response are presented here.
4.1. Measurements of the temporal resolution in ¢shes utilizing the ABR recording technique The ABR recording technique has recently been in-
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
troduced to measure auditory sensitivity in ¢shes (Kenyon et al., 1998). Since then this technique has been exclusively utilized to determine hearing thresholds in ¢shes. This approach yielded invaluable results in intact individuals (Ladich and Yan, 1998; Ladich, 1999) as well as after manipulating ¢sh such as blocking the auditory periphery (Yan, 1998; Kratochvil and Ladich, 2000) or exposing ¢sh to noise (Scholik and Yan, 2001). However, this methodology can also be utilized to measure other characteristics of the auditory system besides hearing thresholds. Popov and Supin (1990) successfully applied the ABR recording technique to investigate the temporal resolution ability of the auditory system in dolphins, especially with regard to their echolocating abilities. In the present study we successfully adapted it to measure the temporal resolution in ¢shes. The approach based on the playing back of double-click stimuli and varying the click periods was also applicable to teleost ¢shes, in particular in groups possessing accessory hearing structures (hearing specialists). When presenting double-click stimuli, two ABR responses were clearly distinguished at click periods longer than 3.5 ms. Temporal resolution data gained by the ABR technique in bottlenose dolphins were similar to those obtained during behavioral tests (Au et al., 1988; Au, 1990; Dubrovskiy, 1990; Popov and Supin, 1990; Supin and Popov, 1995). These observations are supported by comparing our ABR data gained in the present study on otophysine and anabantoid ¢shes to those obtained during behavioral tests in mormyrid ¢shes. P. adspersus di¡erentiated interclick intervals of less than 1 ms (Marvit and Crawford, 2000). ABR control measurements on the mormyrid G. petersii showed minimum resolvable click periods of 0.5 ms (20 dB re HL), which are in good accordance with the behavioral data previously measured in the related genus Pollimyrus. In summary, the reliability of the ABR technique was con¢rmed by the similar response of the auditory system to double-click stimuli in two classes of vertebrates as well as because ABR data are comparable to behavioral data in both taxa. This methodological approach has several advantages. It allows rapid evaluation of the temporal resolution without lengthy training, without killing animals, and without limitations on repeated testing of subjects. 4.2. ABR waveform characteristics Since the present study intended to extend the ABR recording technique to investigate temporal auditory processing, it was important to describe and analyze ABR waveform characteristics in responses to click stimuli. This has not been done so far in ¢shes, and is a prerequisite in order to ¢nd stable reference points
43
and to standardize our analyses. Since the origin of each of the waves remains unclear in ¢shes except for rays (Corwin, 1981), it is not possible to establish a clear correspondence between ABR waves in teleosts and humans. Thus, we did not apply the most common nomenclature of human medicine (in roman numbers) but designated ABR waves by enumerating both the positive and negative peaks similar to Popov and Supin (1990). In dolphins they used ascending arabic numbers. In our study, ABRs in response to click stimuli were very constant between individuals of one species with regard to the shape and latency of the waves. We carefully limited the size range of tested ¢sh in order to avoid variations due to the size (or age) factor. A previous study on croaking gouramis (Wysocki and Ladich, 2001) demonstrated that, beyond individual variations, di¡erences in peak latencies of certain ABR waves and in overall waveform shape also occurred during ontogenetic development within the same individuals, similar to mammals and birds (e.g., Dimitrieva and Gottlieb, 1994; McFadden et al., 1996; Aitkin et al., 1997; Hill et al., 1998). An increase of ABR latency with decreasing SPL is a common phenomenon in ABR measurements and has been described for mammals (e.g., Popov and Supin, 1990; Supin and Popov, 1995) as well as for ¢shes (e.g., Kenyon et al., 1998; Kratochvil and Ladich, 2000). In our recordings the two taxonomic groups seemed to di¡er slightly: wave latency showed a greater intensity dependence in the two otophysans than in the anabantoids. Also, at comparable SPLs, the onset latency of the ABRs was shorter in the anabantoids. This may re£ect di¡erences in auditory processing due to anatomical di¡erences in the peripheral accessory hearing structures, which act as pressure-to-motion transducers. The suprabranchial chamber of the anabantoids directly contacts the saccule of the inner ear in labyrinth ¢shes, whereas in otophysans the swimbladder is connected to the inner ear by a chain of bony ossicles. A dependence of the response amplitude on the stimulus intensity is also a common phenomenon in vertebrate ABRs. This dependence was not linear for the intensity range investigated. At lower stimulus levels the slope of the function was shallower than at higher levels, where it was nearly linear. The function reached asymptotic values at high SPLs only in T. vittata. Supin and Popov (1995) found an intensity dependence of dolphin ABR amplitude until approximately 60^70 dB above HL. We therefore assume that the three other teleost species measured in our study also show an asymptotic amplitude^intensity relationship at higher stimulus levels (we did not record responses to levels above 36 dB re HL). The response to double-click stimuli di¡ered in some
HEARES 3864 2-7-02
44
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
aspects from the recovery function reported in bottlenose dolphins (Popov and Supin, 1990; Supin and Popov, 1995). Whereas the response amplitude to the second click increased steadily with longer interclick intervals in Tursiops truncatus, the response amplitude of the investigated ¢shes showed an irregular increase. This perhaps re£ects di¡erences in auditory processing mechanisms of the nervous system in ¢shes and dolphins, which are particularly specialized to precisely detect consecutive clicks during echolocation. 4.3. Temporal resolution ability of ¢shes Di¡erences in minimum resolvable click periods were observed between species, but no clear trend was found between taxa or vocal species. Whereas in otophysans the vocal cat¢sh showed shorter minimum resolvable click periods, the opposite was true in anabantoids. The temporal resolution ability of these species as revealed by double-click experiments was between 0.3 and 1.4 ms and thus on the average slightly lower than that estimated for dolphins by the same technique (about 0.2^0.3 ms, Supin and Popov, 1995) ; it is, however, within the range of other vertebrate species, where it has been reported to be in the order of several milliseconds (for a review see Fay, 1988). Several authors have stressed the importance of investigating whether the auditory system of ¢shes is capable of resolving the individual pulses within pulsed sounds. This requires in several species a relatively high temporal resolution ability if they do not rely on a general ‘impression’ of sound (Popper, 1972; Hawkins, 1981; Hawkins and Myrberg, 1983). Based on various audiological studies it was assumed that the auditory system of the gold¢sh is particularly well adapted for temporal processing of acoustic stimuli compared to the frequency domain (Fay, 1982). Fishes seem to be able to detect each pulse within a sound, but only few data are available to support these assumptions (Popper, 1972). Temporal resolution has been studied using several di¡erent paradigms, each leading to di¡erent results: Based upon gap detection experiments in ongoing noise, a minimum integration time of about 35 ms was estimated for the gold¢sh (Fay and Coombs, 1984), a value considerably larger than in mammals and birds (2^4 ms; see Fay, 1985). On the other hand, behavioral and neural temporal modulation transfer functions for noise and tones based on sinusoidal amplitude modulations suggested an integration time of less than 0.4 ms in the gold¢sh (Fay, 1980). In another study, Fay et al. (1983) revealed that gold¢sh are able to detect changes of about 6^7% at echo delays in noise between 1.25 and 10 ms. For this detection of echo delays they suggested a limitation of about 1 ms due to the refractory period of saccular units. These data are comparable to the
minimum resolvable pulse period of about 1.25 ms we found in gold¢sh. The latter type of stimulation (repeated noise with delay in the onset) may also approximate our double-click stimuli paradigm. Our stimulus, consisting of short, broad-band pulses with a fast rise time, might not be suitable to investigate temporal resolution of the auditory system in hearing generalists because their narrower hearing band width would probably not yield fast rises in the stimulus waveform as does the wider band width of hearing specialists. Our knowledge of the temporal resolution in other ¢sh species and taxa is poor, especially in vocal ones where acoustic signals are important for communication. Besides the above-mentioned data from the mormyrid Pollimyrus, there is only evidence from behavioral discrimination tasks that damsel¢sh of the genus Pomacentrus must be capable of distinguishing temporal di¡erences of sounds between at least 5 and 10 ms (Myrberg et al., 1978). Altogether, teleost ¢shes seem to have temporal resolution abilities in the order of a few milliseconds or even less, which is not fundamentally di¡erent from other vertebrates such as mammals and birds. 4.4. Comparison between the temporal resolution and temporal structure of sounds The sound analysis of the two vocalizing species showed that pulse periods varied especially in P. costatus. Comparing pulse intervals of conspeci¢c sounds to the minimum resolvable click period, the auditory system of T. vittata clearly processes each of the pulses within conspeci¢c sounds separately. Naturally occurring sounds have SPLs which are within the range tested or higher. Even considering that the time resolution capability decreases with increasing SPL, it is very likely that double pulses and single pulses can be detected. The pulse periods of P. costatus’ stridulatory sounds are quite variable. Most values indicate that pulses within a sound can be processed separately by the auditory system of this cat¢sh species. Our analysis of over 700 pulses revealed that only three values (in merely one individual out of eight) were below the minimum click period resolvable at low SPLs. Therefore, we compared the levels used in this study with SPL measurements of stridulatory sounds of P. costatus in a previous study (Ladich, 1999). Those levels were up to 15 dB higher than our maximum level tested. Because in this species the minimum resolvable click period decreased with increasing dB level re HL, the auditory system of the ¢sh can probably process almost all pulses within a sound, especially because ABR waves only re£ect the ¢rst steps of auditory processing in the
HEARES 3864 2-7-02
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
brainstem up to the midbrain (Corwin, 1981), and ‘higher’ levels of the central nervous system might improve temporal resolution. Grunts of the mormyrids Pollimyrus isidori and P. adspersii mainly di¡er in their interclick interval, whereas another type of sound they produce di¡ers primarily in its dominant frequency. Both sounds play a role in the mating system of the ¢sh. Marvit and Crawford (2000) concluded from behavioral audiological experiments that discrimination thresholds in the mormyrids are su⁄cient to mediate species and maybe individual recognition as well. Behavioral tests in damsel¢sh (Myrberg et al., 1978) showed that their ability to discriminate acoustically between closely related sympatric species relied primarily on the pulse period of the sounds. Summarizing the sparse available data on auditory temporal resolution, the auditory capabilities of teleost ¢shes (at least of hearing specialists) are probably su⁄cient to process pulses within sounds separately. Temporal patterns of sounds can thus provide reliable information during acoustic communication. These data are in agreement with behavioral observations and the structure of many ¢sh sounds. Furthermore, these capabilities do not represent a special adaptation to intraspeci¢c communication because they are also observed in non-vocal species. Rather, these abilities rely on the properties of the auditory system and on the temporal processing by the nervous system.
Acknowledgements We would like to thank Brigitte WeiM for assistance during this study and two anonymous reviewers for critically reading the manuscript. This study was supported by the Austrian Science Fund (FWF Grant No. 12411 to F.L.).
References Aitkin, L., Cochran, S., Frost, S., Martsi-McClintock, A., Masterton, B., 1997. Features of the auditory development of the short-tailed Brazilian opossum, Monodelphis domestica: evoked responses, neonatal vocalizations and synapses in the inferior colliculus. Hear. Res. 113, 69^75. Au, W.W.L., 1990. Target detection in noise by echolocating dolphins. In: Thomas, R.A., Kastelein, R.A. (Eds.), Sensory Abilities of Cetaceans. Laboratory and Field Evidence. Plenum Press, New York, pp. 203^216. Au, W.W.L., Moore, P.W.B., Pawloski, D.A., 1988. Detection of complex echos in noise by an echolocating dolphin. J. Acoust. Soc. Am. 83, 662^668. Corwin, J.T., 1981. Audition in elasmobranchs. In: Tavolga, W.N., Popper, A.N., Fay, R.R. (Eds.), Hearing and Sound Communication in Fishes. Springer, New York, pp. 81^102.
45
Crawford, J.D., 1997. Hearing and acoustic communication in mormyrid electric ¢shes. Mar. Freshw. Behav. Physiol. 29, 65^86. Dimitrieva, L.P., Gottlieb, G., 1994. In£uence of auditory experience on the development of brain stem auditory-evoked potentials in mallard duck embryos and hatchlings. Behav. Neurol. Biol. 61, 19^28. Dolphin, W.F., 1997. Electrophysiological measures of auditory processing in odontocetes. Bioacoustics 8, 79^101. Dubrovskiy, N.A., 1990. On the two auditory systems of dolphins. In: Thomas, R.A., Kastelein, R.A. (Eds.), Sensory Abilities of Cetaceans. Laboratory and Field Evidence. Plenum Press, New York, pp. 233^254. Fay, R.R., 1980. Psychophysics and neurophysiology of temporal factors in hearing by the gold¢sh: Amplitude modulation detection. J. Neurophysiol. 44, 312^332. Fay, R.R., 1982. Neural mechanisms of an auditory temporal discrimination by the gold¢sh. J. Comp. Physiol. A 147, 201^216. Fay, R.R., 1985. Temporal processing by the auditory system of ¢shes. In: Michelsen, A. (Ed.), Time Resolution in Auditory Systems. Springer, Berlin, pp. 28^57. Fay, R.R., 1988. Hearing in Vertebrates: A Psychophysics Databook. Hill-Fay Associates, Winnetka, IL. Fay, R.R., Coombs, S.L., 1984. Sound intensity processing by the gold¢sh auditory system. J. Acoust. Soc. Am. 76, S12. Fay, R.R., Yost, W.A., Coombs, S.L., 1983. Psychophysics and neurophysiology of repetition noise processing in a vertebrate auditory system. Hear. Res. 12, 31^55. Gerald, J.W., 1971. Sound production in six species of sun¢sh (Centrarchidae). Evolution 25, 75^87. Gorga, M.P., Kaminski, L.R., Beauchaine, K.A., Jestaedt, W., 1988. Auditory brainstem response to tone bursts in normally hearing subjects. J. Speech Hear. Res. 31, 87^97. Hall, J.W., 1992. Handbook of Auditory Evoked Responses. Allyn and Bacon, Boston, MA. Hawkins, A.D., 1981. The hearing abilities of ¢sh. In: Tavolga, W.N., Popper, A.N., Fay, R.R (Eds.), Hearing and Sound Communication in Fishes. Springer, New York, pp. 109^133. Hawkins, A.D., Rasmussen, K.J., 1978. The calls of Gadoid ¢sh. J. Mar. Biol. Assoc. UK 58, 891^911. Hawkins, A.D., Myrberg, A.A., Jr., 1983. Hearing and sound communication under water. In: Lewis, B. (Ed.), Bioacoustics, a Comparative Approach. Academic Press, London, pp. 347^405. Hill, K.G., Cone-Wesson, B., Liu, G.B., 1998. Development of auditory function in the tammar wallaby Macropus eugenii. Hear. Res. 117, 97^106. Kenyon, T.N., Ladich, F., Yan, H.Y., 1998. A comparative study of hearing ability in ¢shes: the auditory brainstem response approach. J. Comp. Physiol. A 182, 307^318. Kileny, P., Shea, S.L., 1986. Middle-latency and 40-Hz auditory evoked responses in normal-hearing subjects: clicks and 500 Hz thresholds. J. Speech Hear. Res. 29, 20^28. Kratochvil, H., 1985. Beitra«ge zur Lautbiologie der Anabantoidei ^ Bau, Funktion und Entwicklung von lauterzeugenden Systemen. Zool. Jahrb. Physiol. 89, 203^255. Kratochvil, H., Ladich, F., 2000. Auditory role of lateral trunk channels in cobitid ¢shes. J. Comp. Physiol. A 186, 279^285. Ladich, F., 1997a. Agonistic behavior and signi¢cance of sounds in vocalizing ¢sh. Mar. Freshw. Behav. Physiol. 29, 87^108. Ladich, F., 1997b. Comparative analysis of swimbladder (drumming) and pectoral (stridulation) sounds in three families of cat¢shes. Bioacoustics 8, 85^208. Ladich, F., 1998. Sound characteristics and outcome of contests in male croaking gouramis (Teleostei). Ethology 104, 517^529. Ladich, F., 1999. Did auditory sensitivity and vocalization evolve independently in otophysan ¢shes? Brain Behav. Evol. 53, 288^304.
HEARES 3864 2-7-02
46
L.E. Wysocki, F. Ladich / Hearing Research 169 (2002) 36^46
Ladich, F., Yan, H.Y., 1998. Correlation between auditory sensitivity and vocalization in anabantoid ¢shes. J. Comp. Physiol. A 182, 737^746. Ladich, F., Bischof, C., Schleinzer, G., Fuchs, A., 1992. Intra- and interspeci¢c di¡erences in agonistic vocalization in croaking gouramis (genus: Trichopsis, Anabantoidei, Teleostei). Bioacoustics 4, 131^141. Mann, D.A., Lobel, P.S., 1997. Propagation of damsel¢sh (Pomacentridae) courtship sounds. J. Acoust. Soc. Am. 101, 3783^3791. Marvit, P., Crawford, J.D., 2000. Auditory discrimination in a soundproducing electric ¢sh (Pollimyrus): tone frequency and click-rate di¡erence detection. J. Acoust. Soc. Am. 108, 1819^1825. McFadden, S.L., Walsh, E.J., McGee, J., 1996. Onset and development of auditory brainstem response in the Mongolian Gerbil (Meriones unguiculatus). Hear. Res. 100, 68^79. McKibben, J.R., Bass, A.H., 1998. Behavioral assessment of acoustic parameters relevant to signal recognition and preference in a vocal ¢sh. J. Acoust. Soc. Am. 104, 3520^3533. Myrberg, A.A., Jr., Spires, J.Y., 1972. Sound discrimination by the bicolor damsel¢sh, Eupomacentrus partitus. J. Exp. Biol. 57, 727^735. Myrberg, A.A., Jr., Spanier, E., Ha, S.J., 1978. Temporal patterning in acoustic communication. In: Reese, E.S., Lighter, F.J. (Eds.), Contrasts in Behaviour. John Wiley and Sons, New York, pp. 137^179. Myrberg, A.A., Jr., Mohler, M., Catala, J.D., 1986. Sound production by males of a coral reef ¢sh (Pomacentrus partitus): its signi¢cance to females. Anim. Behav. 34, 913^923. Pfei¡er, W., Eisenberg, J.F., 1965. Die Lauterzeugung der Dornwelse
(Doradidae) und der Fiederbartwelse (Mochokidae). Z. Morph. º kol. Tiere 54, 669^679. O Popov, V.V., Supin, A.Y., 1990. Auditory brain stem responses in characterization of dolphin hearing. J. Comp. Physiol. A 166, 385^393. Popper, A.N., 1972. Auditory threshold in the gold¢sh (Carassius auratus) as a function of signal duration. J. Acoust. Soc. Am. 52, 596^602. Pruzsinszky, I., Ladich, F., 1998. Sound production and reproductive behaviour of the armoured cat¢sh Corydoras paleatus (Callichthyidae). Environ. Biol. Fish. 53, 183^191. Scholik, A.R., Yan, H.Y., 2001. E¡ects of underwater noise on auditory sensitivity of a cyprinid ¢sh. Hear. Res. 152, 17^24. Supin, A.Y., Popov, V.V., 1995. Temporal resolution in the dolphin’s auditory system revealed by double-click evoked potential study. J. Acoust. Soc. Am. 97, 2586^2593. Winn, H.E., 1964. The biological signi¢cance of ¢sh sounds. In: Tavolga, W.N. (Ed.), Marine Bioacoustics, Vol. 2. Pergamon Press, New York, pp. 213^231. Winn, H.E., 1967. Vocal facilitation and the biological signi¢cance of toad¢sh sounds. In: Tavolga, W.N. (Ed.), Marine Bioacoustics, Vol. 2. Pergamon Press, New York, pp. 283^303. Wysocki, L.E., Ladich, F., 2001. The ontogenetic development of auditory sensitivity, vocalization and acoustic communication in the labyrinth ¢sh Trichopsis vittata. J. Comp. Physiol. A 187, 177^ 187. Yan, H.Y., 1998. Auditory role of the suprabranchial chamber in gourami ¢sh. J. Comp. Physiol. A 183, 325^333.
HEARES 3864 2-7-02