The auditory system of the goldfish (Carassius auratus): Effects of intense acoustic stimulation

Camp Bmchem Phymol. 1976. Vol 53A. pp 11

to

18 Pergamon Press Printed m Great Britain

THE AUDITORY SYSTEM OF THE GOLDFISH (CARASSIUS AURATUS): EFFECTS OF INTENSE ACOUSTIC STIMULATION* ARTHUR N. POPPER AND NANCY L. CLARKE Department of Zoology and Laboratory of Sensory Sciences, University of Hawaii, Honolulu, HI 96822, U.S.A

(Reeewed 17 December 1974) Abstract--l. Behavioral investigations were made of the effects of intense pure tone stimulation on auditory thresholds for the goldfish (Carassius auratus). 2. Results indicate that different sumulation frequencies have a different effect on the test frequencies whde each of the test frequencies had the same degree of threshold shift after stimulation to each of the stimulation frequencies. 3. Results are interpreted to indicate that the teleost inner ear responds m a relatively complex fashion to different stimulating frequencies and this may indicate some degree of spatial signal analysis m the inner ear.

INTRODUCTION

BEHAVIORAL investigations have shown that significant signal analysis and processing, analogous in some ways to aspects of auditory processing in mammals, is occurr|ng in the teleost auditory system. Evidence for this includes the capabilities of a number of species to perform frequency discrimination (Dijkgraaf & Verheijen, 1950; Fay, 1970; Jacobs & Tavolga, 1968; Stetter, 1929) and the ability of at least one species to do intensity discrimination (Jacobs & Tavolga, 1967). Auditory masking has also been demonstrated m a number of species (Buerkle, 1968; Cahn et al., 1970; Enger, 1973; Tavolga, 1967, 1974) and recently, Tavolga (1974) has demonstrated a critical band-like mechamsm in the goldfish (Carassius auratus). Tavolga also provided evidence that a similar mechanism may not be present in several other species. Further support for a relatively complex processing system comes from several physiological experiments. Enger 0963) and Furukawa & Ishii (1967) have shown that there are at least two different classes of neurons coming from the tuner ear of several teleost species, and Page (1970)and GrSzzinger (1967) have demonstrated the presence of different types of response neurons at different levels of the central nervous system associated with audition. Enger 0973) has also recently demonstrated the presence of maskmg effects at the level of the medulla in goldfish. While the behavioral and physiological data provide some information about the types of processing occurring in the teleost ear, data on the mechanism(s) and site(s) for this processing of acoustic information are not concluswe. Arguments have been presented for some processing in the inner ear (of. van Bergeijk, 1967a, b; Sand, 1974; Tavolga, 1974; and others) * Send request for reprints to Dr. A. N. Popper, Laboratory of Sensory Sciences, University of Hawaii, 1993 EastWest Road, Honolulu, HI 96822, U.S.A.

although the morphology of the ear does not provide a clear mechanism for any currently known analysis system. Furthermore, in light of the wide variation in morphology found in the ears of different species (see reviews by Lowenstein, 1971; Popper & Fay, 1973; Tavolga, 1971), it is not inconceivable that there are different types of processing systems m different species. In addition to variations in the gross morphology of the ear there is recent evidence for differences in the functioning of the auditory structures peripheral to the inner ear. Fay & Popper (1974, 1975) have demonstrated that the path for sound to the inner ear in the Ostariophysi, a group of about 5000 primarily freshwater fishes with a series of bones, the Weberian ossicles, coupling the swimbladder to the inner ear, is significantly different than in non-ostariophysines. Fay & Popper have also shown that in at least two species of ostariophysines (Carassius auratus and lctalurus punctatus), representing different taxonomic families, sound is detected by the swimbladder and carried to the inner ear via the Weberian ossicles. In one non-ostariophysine (Tilapia macrocephala), however, the swimbladder has no role in sound detection and sound travels to the inner ear through bone conduction (Fay & Popper, 1975). These data, coupled with the fact that the saccular otolith (a dense calcareous bone overlying the hair cells of the auditory portion of the inner ear in fishes) is large in non-ostariophysines but small and fluted in ostariophysines, suggests that some as yet unknown aspects of acoustic processing, as well as detection, may differ at least between these two major "groups" of fishes. The present study is addressed to the question of sound processing by the goldfish. Rather than use a behavioral analysis based upon measures of discrimination, however, we have applied a procedure involving intense acoustic stimulation to alter, temporarily, acoustic sensitivity and to determine whether different pure tones produce sensitivity decrements at all frequencies or at specific frequencies. Under certain con-

12

ARTHURN. POPPERAND NANCYL. CLARKE

ditions of low stimulation intensity and low frequencies (below 1000I-Iz) these types of data hve provided an indication of spatial analysis in the mammalian cochlea by selectively causing greater degrees of threshold change at frequencies that are in some way related to the stimulation frequency (Benitz et al., 1972; Davis et al., 1952; Hunter-Duvar & Elliot, 1972; Poche et al., 1969). It has been our intention to use this stimulation method to determine (1) whether there is any indication of spatial analysis of frequency at some level of the teleost auditory system and (2) whether there is any similarity between the mammalian and teleost response to intense tones. The procedures used in the current experiments were modified from methods used for studying temporary threshold shift fITS) in mammals where intense tonal stimulation is given for a set period of time and then followed within several minutes or seconds by threshold determination to find if there has been a shift in auditory sensitivity (see Elliot & Fraser, 1970; and Ward, 1953, for reviews). The procedures were modified since it was impossible to make threshold determination immediately after the end of the intense stimulation due to the slow behavioral response system in fishes. Therefore, the data tend not to show rapid changes in threshold shift (occurring within several seconds of the end of stimulation) but long-term auditory fatigue that may last for several hours, or even days (see Selters, 1964; Young & Sachs, 1973).

MATERIALS AND METHODS

Changes in auditory thresholds due to intense sound stimulation were determined for goldfish (Carasstus auratus) 40-120mm in standard length obtained from commercial sources or from the Nuuanu Reservoir, Oahu, Hawaii. Behamoral testing Auditory thresholds were determined using (1)avoidance conditioning and threshold tracking, or (2) classical conditioning of respiratory suppression and method of limits. Different techniques were used due to changes in certain laboratory facilities. However, experiments demonstrate that both techniques provide completely comparable results (Popper et al., 1973). The avoidance conditioning and tracking procedure has been described previously (Jacobs & Tavolga, 1967, 1968; Popper, 1970, 1971)and will only be discussed briefly here. Ammals were trained to indicate the presence of a pure tone by crossing a submerged bamer separating two small chambers in a plexiglass tank (Fig. I), thus breaking a beam of light to a photocell. The response of the photocell was monitored by programming equipment that also controlled the timing, sound presentation, and shock presentation during each trial as well as monitoring the response of the animal during the intertrml period. If the animals crossed the barrier within 10sec of the sound onset the trial was terminated and the sound level was lowered by several dB for the next trial. If, instead, the ammal thd not respond within 10sec it recewed a mild electric shock (generally 5- I0 V a.c at the source, 50 msec long) one per sec until it crossed the barrier. The sound

~'~ a~--Cove

Sand

r

Wood box Electrode Test box - -

Barrier

Foam Rubber Sand

A

I_

d

Cement block

r

Wood box Electrode Speaker

lest box Photocell

Light for photocell |

R e f r i g e r a t o r outer w a II

Sand 2 0 cm

e

I

I

Fig. 1. Test tank and acoustic chamber used in avoidance conditioning experiments. The acoustic chamber was an old refrigerator with an inner wooden box. The space between the wood box and the refrigerator walls was filled with sand. A. Side view of the test tank. B. Top view of the experimental set-up. The same acousUc chambers were used for the classical conditioning experiment and the test tank was essentially the same as in the avoidance experiments except that the barrier was not present and small support rods were present for the fish holder and phonograph cartridge (from Popper, 1971).

The auditory system of the goidfish

"10

FISH ' O 123 TEST FREQ. * BOOHz STIM. DUR. t 4 Hri

W f

13

I

l t t

l -15

t t I

-20

STIM. 800 Hat, 46 dg

I^

-25

-~ -3o

STIM. z 500 Hz, 49 dB

i "~ -4o

f nME (,,~N)

Fig. 2 Typzcal threshold determination sessions for fish O123 All of the tests were at 800Hz. Inmal determinations were made using changes in signal level of 5 dB but this was switched to 1 dB steps after an initml warm-up period. An upward change m the curve indicates that the animal had not indicated detection of the prewous signal while a downward sloping line indicates that the animal had detected the prewous signal.

level for the next trml was then raised by several dB Auditory thresholds were calculated at a 50% level using the up-down staircase method (tracking) with 15-20 changes between sound detection and no-detection averaged for a threshold determination for each day for each animal. Typical determinations are shown in Ftg 2 where changes in direction upwards indicate that the animal had not detected a sound while a change downward indicates that the animal had detected the sound. Conditioned suppression consisted of training the animals to temporardy suppress the rate and/or amplitude of respiration during the presentation of a pure tone conditioned stimulus (CS) by pairing the sound with a single shock which followed the 10sec CS. The uncondttioned response to the shock was a suppression of respiration, generally lasting 1-3 see. After several pairings of sound and shock (often as few as five) the animals showed suppress~on to the sound alone. Respiration was measured by placing a 2.54em dia screen paddle lightly in contact with the ammal's mouth. A thin metal rod from the paddle was inserted into a phonograph cartridge which responded to the motion of the paddle with an analog output that was fed into an mtegrator (Woodward, 1972) which produced a digital output proportional to the respiration rate and amplitude. The output was recorded (on a digital recorder which was part of the control system) during the 10see immediately prior to sound presentation and during the 10see sound presentation. The degree of respiration suppression during the sound period was calculated by taking the ratio of the number of integrator pulses during the sound period to the sum of the pulses during the total 20 see period. This suppression ratio (SR) was about 0-50 when there was no suppression during sound stimulation and less than 0"50 when there was a change in respiratory pattern. The criterion level for a response during the sound presentation was an SR of 0"44. This criterion SR was determined by

measuring the SR's during 500 trials in which there was no sound presented during the trial period (these blank trials alternated with stimulus trials throughout the suppresslon procedure). The mean SR for the 500 blank trials was 0'51 + 0.035. The criterion SR was two standard deviations from the mean and continued calculation of the SR's during blank after the init,al 500 trials showed that only in the rarest circumstances were the SR's ever at or below 0-44 when sounds were not present. In order to measure respiration accurately during the classical conditioning procedure, the animals were loosely restrained in a cheesecloth holder (see Popper et al., 1973) which kept the animals in the same relative position to the paddle, sound field, and shock electrodes. Testing was done using a modified method of limits. The initial sound level in a series of trials was 20-30dB above the normal threshold and the SPL was lowered by 5 dB in each of 7-8 successive trials The SR was calculated for each of the trials in a series and the 50% threshold point was the value between the sound level where the animal changed from detecting the sound (SR < 0.44) and where the animal no longer detected the sound (SR > 0-44) in two successive trials. After the series of trials the SPL was reset to the initial level and the series run again. This was generally repeated at least six times in I day with the threshold for that day taken as the mean value for the six series of trials. This method, rather than traeking~ had to be used for the classical conditioning due to limitation in the control equipment. For a similar reason we could only run trials down (lowering the SPL) rather than having alternate series starting above and below the threshold.

Test procedure After the animals had achieved a level of 90°/, correct responses for several days, their thresholds were determined for 1-2 weeks at 500 or 800 Hz ha order to provide overtraining before placing them in the "ITS situation.

14

ARTHUB~]. POPPERAND NANCYL. Ct~RKE

If this was not done, and the animals were placed into a situation with high intensity stimulation, they would frequently 'fail to respond in threshold tests. Each test sequence generally lasted 3 days with sever:el days of rest between each sequence. On day 1 the animal's normal auditory threshold was determined. On day 2 the animal was placed into a small aquarium in a soundproof chamber and received pure-tone stimulation for 4 hr. This was followed by threshold determination for the next 2 hr. On day 3 the animal's threshold was again determined without prior stimulation. If the threshold was not equivalent to the level on day ! the animal was tested on successive days until the threshold was normal. In almost all eases, except for initial tests with stimulation intensities above those finally used in the experiments, the ammals returned to normal threshold within 24 hr of stimulation.

Sound stimulation and control The test sounds were pure tones generated with an audio generator (Heathkit model IG-18), gated through an electronic switch (Grason-Stadler 829E), filtered (Krorhn-Hite model 3500) to remove switch transients, attenuated (Daven precision attenuators) and amplified (Dyna stereo 120 amplifier). The sounds were presented through atr loudspeakers. Thresholds were deterrmned in soundproof chambers (see Popper, 1971) and the ambient sound levels in these chambers were substantially below threshold so there was no possibility of masked thresholds. The stimulation with intense sounds were done using an audio generator and amplifier and the sound was delivered through a driver (University) placed above the water in the st,mulation chamber. Sound stimulation consisted of pure tones at 300, 500, 800 and 1000Hz and testing was conducted at 500 and 800 Hz in order to determ,ne the effects of different frequency stimulation on the tel;t frequency response. During most of the experiments the sound pressure level for the stimulation was 49 dB (re: 1 tthar) (equivalent to 123 dB re: 0.0002/~har). In several additional experiments the stimulation was 49dB (re: 1/ab) (equivalent to 123dB re: 0.0002/~b). In several additional exper,ments the threshold shift. Calibration Sounds were measured in the test tank using a hydrophone (Clevite model CH-17T) placed at various points in the tanks. The sound pressure variation in the avoidance tank was generally +4dB and it has been found that the fish give consistent thresholds since they always tend to swim into the areas of maximum sound level (Jacobs & Tavolga, 1967; Popper, 1970). The sound pressure for the classical conditioning experiment was measured along the length of the ammal and did not vary by more than +2riB. The sound pressure in the stimulation chamber, where the animal could freely swim around, was +2dB throughout the tank. RESULTS Experiments were conducted with 25 animals, with at least 4 animals used for each combination of test tone, stimulation tone, and stimulation intensity. Data using the avoidance conditioning were comparable in all test conditions where both were used (P > (~5 in all cases) and so data are pooled (see Popper et el., 1973, for comparison of methods). In all cases the stimulation sound pressure levels were plotted for each trial over the 2 hr period of testing in order to determine if there were any time dependent trends in the threshold changes such as decreases in threshold with time. No such trends were

T h r u h o l d o determXned a c e a c h c u t

T~SLS 1 .

at 8evezll A.

Tut

Jtl~ltcton

Y r e q u n c y - 500 Rz

S e t u u l a t Lou

freqtutacy (lit)

SPI,

Mean

(dE r e :

threllmld

1 ~bar)

(dS r e . 1

None

B

frequency alter etLmetetto. at different ~.ntensttie8.

frequencLee

pb,rp

-41

T-Tent N

S.D.

147

8.02

16

(re n o n - s t t u u l s t i ~ )

300

49

-33 I

6 12

p o

027

500

52

-30.1

16

8 59

p -

004

$00

49

-32.1

22

7.33

p <.001

$00

t6

-33.2

&2

7 23

p <.001

500

43

-43.6

11

5 73

p >.05

300

37

-45 A

14

9 81

p • 05

800

49

-23 7

13

3.83

p • 001

1000

49

-24 9

21

6 74

p < 001

Test Prequency - 800 I~ Noue

-39 7

120

7 95

300

A9

-36.4

10

8.20

500

52

-28 3

$

12.47

p <.001

500

49

-32 3

18

11.11

p - 033

800

49

-11.4

8

6.91

p <.001

800

46

-16 4

4

5.79

p < 001

800

37

-23.7

12

7.53

p <.OOZ

800

32

-29.8

4

4.35

p <.OOI

1000

49

-23 2

23

15 26

p <.001

p >.05

found and so data over the 2 hr test period were averaged after an initial warm-up time of 10--20min. Several typical determinations are shown in Fig. 2 for test animal GI23. A normal determination is shown for 800Hz along with threshold determinations at 800 Hz after st]mulat]on at 500 and 800 Hz. The normal threshold was -41.3 dB (re: I/~bar) (35 changes) while after 500 Hz stimulation the mean threshold was -33.4dB/ab (36 changes) and after 800Hz stimulation the threshold was -22.3 dB (28 changes). The results of stimulation at various frequencies and testing at 500 or 800 Hz are presented in Table 1, and the data are summarized in Fig. 3 as amount of threshold shift relative to normal thresholds. Thresholds determined at 500 and 800 Hz without stimulation (--41 dB/~b for 147 determinations and -39.7 dB/~b for 120 determinations respectively) are comparable to thresholds for the goldfish determined previously in thin and other laboratories (Fay, 1969; Jacobs & Tavolga, 1967; Popper, 1971). After stimulation at 300 Hz, the 500 Hz threshold shifted to -33.1 dB#b, a significant difference from the non-stimulated threshold (P = 0.027, Student's t-test). Stimulation at all of the other frequencies resulted in significantly different 500 Hz thresholds than the non-stimulated thresholds (see Table 1). Control experiments with the animals placed in the stimulation chamber without the intense sound, followed by testing, showed that the experience in the stimulation chamber was not the cause of the threshold ,shifts. This was further substantiated by the threshold tests after stimulating at 500 Hz at 37 and 43 dB/ab, where there was no statistically significant threshold shifts. Similar results were found with testing at .800 Hz except that the threshold shift after stimulation at 300 Hz was not significant ~(P = 0.337) while stimulation at the other frequencies showed significant

The auditory system of the goldfish

+5 0 37 • 43

•

15

TEST FREQUENCY 500 Hz

0 8 0 0 Hz

0¸ --5"

•

46

--10 "

I--15 ~S

"

52 •

0 32

-

_2o.

~ , ~ --30 -

3~o

s~o Stimulation

a~o

1~oo

Frequency (Hz)

Fig. 3. Amount of threshold shift (vrs) at 500 and 800 Hz test frequencies for each of the stimulating frequencies. Lines connect the levels of "ITS after stimulation at 49 dB (re: 1 Fbar) and additional points show the effects of stimulation at the indicated intenmies (all in dB re: 1/zbar). threshold shifts. Testing after different 800 Hz stimulation intensities resulted in significant threshold shifts even when the stimulation level was as low as M dB/zb, DISCUSSION Several p o i n t s are i m m e d i a t e l y a p p a r e n t f r o m o u r

data concerning the effects of intense sonic stimulation. First, it is clear that the amount of threshold shift produced by each stimulating frequency is not the same. For example, the shift produced at 500 Hz by the 300 Hz stimulation (49 dB/zb) tone was about 8 riB, while 800 I-Iz stimulation (49 dBFb) produced a 17.3 dB threshold shift at 500 Hz. Similar effects were caused by each stimulating frequency on the 800 Hz test signal. A second point is that the degree of threshold shift produced by different stimulating frequencies are roughly grouped. Stimulation at 300 and 500 Hz produced markedly different threshold shifts than stimulation at 800 and 1000 Hz. However, the shifts caused by 300 and 500 Hz stimulation are approximately the same at both of the test frequencies as are the shifts caused by stimulation at 800 and 1000 Hz. A third point is that the amount of threshold shift caused by each individual stimulating frequency was approximately the same at both test frequencies with the exception of stimulation and testing at 800Hz. Before considering the mechanisms and implications of these data it is important that we have some idea of the site of the temporary threshold shift in the goldfish. A variety of evidence, albeit mostly circumstantial, suggests that the actual level for the temporary threshold shift in the goldfish is in the sacculus. This is based upon consideration of what is known about the function of various levels in the

teleost auditory system (see Lowenstein, 1971; Popper & Fay, 1973; Tavolga, 1971 for reviews) as well as data on the site for temporary threshold shift in mammals. In considering the various parts of the teleost auditory system it is probable that we can eliminate the structures peripheral to the inner ear from involvement in the "ITS. The sound detecting structure, the swimbladder in goldfish (see Fay & Popper, 1974), has an essentially fiat frequency response from 50 Hz to over 2000Hz (Popper, 1974) and it is unlikely that this strictly mechanical system would differentially fatigue to different stimulus tones. Again, the Weberian ossicles, bones coupling the swimbladder to the inner ear, are a mechanical system that probably does not respond differently to varying frequencies, at least in the frequency range used in our experiments. Although direct experimental data are lacking, recent investigations of microphonic responses from the goldfish sacculus have shown the same level of response to equal stimulation from 300 to 800 I-Iz (Fay & Popper, 1974), suggesting that the pass band of the Weberian ossicles (and swimbladder) is flat at least over this range. While the auditory system central to the inner ear in teleosts is poorly known, it is possible either that differential fatigue is present in individual neurons of these centers or, that there are different groups of neurons that respond to different frequencies and which fatigue after continuous intense stimulation. Experiments by Page (1970) and Gr~zzinger (1967) have shown that the central auditory system in fishes has variable responses in different regions although these workers found no evidence (in two species) for any tonotopic organization of the response to pure tone stimulation of the fish. In addition, experiments on the mammalian 8th nerve has shown that at least

16

ARTHUR N. POPPER AND NANCYL. Ct.ARKE

this group of neurons has a rapid recovery (measured in minutes rather than hours)" from intense stimulation (Young & Sachs, 1973). This suggests (although by no means proves) that central auditory neurons would recover rapidly from over-stimulation and not be responsible for the temporary threshold shift in fishes. "' While direct evidence indicating that the site of teleost T r s are lacking, experiments in mammalian systems have shown that one effect of intense acoustic stimulation is to morphologically and physiologically affect the hair cells of the inner ear (Davis et al., 1953; Price, 1972; Wever & Lawrence, 1955) and it is possible that the homologous teleost hair cells would be affected in similar ways by intense stimulation. If the likely site for the temporary threshold shift is the inner ear of the goldfish, it is then necessary to provide a functional basis for the phenomena and to try and use our data to provide some information about the processing mechanism at the level of the inner ear. Several mechanisms are suggested by various aspects of the data including a volley-type as well as a more complex place system, which, while not approaching a place system as described for mammals, may provide at least some degree of frequency processing using spatial analysis. A major point supporting a volley-type of system is the finding that both of the test frequencies were affected in the same way by each of the stimulating frequencies. This would be expected under conditions where each stimulating frequency affects all of the hair cells in the inner ear at an equal level" and where many or all of the neurons in the 8th nerve respond to a broad range of stimulating frequencies. However, the finding that the degree of threshold shift caused by the individual stimulating frequencies is not equal tends to argue against stimulation of the whole ear for all frequencies. Consequently, we would suggest that the analysis system of the teleost ear is more complex than one would find in a simple volley-type of system. Instead, we might hypothesize that the results, showing a different degree of threshold shift with different frequencies, indicate a more complex system that would involve relatively "discrete" portions of the response system for different frequencies. This might be explained by suggesting a place-type of mechanism in the teleost ear similar to, but probably less discrete than, that found in the mammalian ear. However, morphological considerations argue against this type of system (see Popper & Fay, 1973, for review), at least in terms similar to those discussed for mammals. The sacculus has an oval, hair cell covered, membrane that is overlain by a dense calcareous otolith. Stimulation of the hair cells is thought to occur by a shearing action between the otolith and the hair cells with the necessary differential motion between the two structures set-up during sound stimulation. The hair cells are of approximately the same density as water, and as a result the otolith and the hair cells respond differently to stimulation. While this system does not provide the basis for a frequency analysis system such as in mammals there are several possible methods through which at least some degree of signal analysis could occur using different regions of the 'sensory macula to respond to different frequencies. Van 13ergeijk (1967a) has proposed that such a

system could be possible if the sensory macula were worked in an analogous fashion to the head of a "bongo drum" with different modes of vibration set up for different stimulating frequencies. This system would only work in an assymetrieally taut membrane, such as the saccular macula, although measurements have not actually been made to determine if this mechanism ~s possible in the fish ear. With such a system, different portions of the macula would respond to different frequencies although it is not necessary that contiguous sections respond to contiguous frequencies. In fact, several points along the macula might respond to the same frequency. This type of mechanism has been demonstrated along the tympanic membrane of cats by Khanna & Tonndorf (1972) using holographic techniques and similar results are reported in locusts by Michelson (1971). The holographic analyses also have shown that as stimulating intensity increases the area of stimulation also increases as nodes around a central point. This type of mechanism would allow for greater hair cell involvement, and fatigue of more hair cells, as stimulation intensity increased. The result would be greater temporary threshold shift with sumulation intensity increase, such as found m our data for different stimulation intensities. Another possible mechanism is based upon variation in the movement of the otolith as a consequence of fluting and its generally uneven surface (Sand, 1974). This would result in the otolith stimulating different groups of hair cells at different frequencies and would perhaps be most suitable in otoliths where there is a controlled direction for inner ear stimulation, such as from the swimbladder. However, in species where sound stimulation is directly through bone stimulation (as in Tilapia macrocephala, Fay & Popper, 1975) energy would come from no specific direction and, as a result, there would not be a consistent pattern of otolith stimulation for different frequencies (Sand, 1974). If a spatial system was functioning in the goldfish ear, we would expect, as found, that different stimulating frequencies would potentially produce different degrees of threshold shift. It would also be predicted that maximum threshold shift would occur with testing and stimulation at the same frequencies, as has occurred at 800 Hz. However, a similar phenomenon did not occur with stimulation and testing at 500Hz, and the maximum shift at 500Hz was when stimulation was at both 500 and 800 Hz. This then suggests a "modified" spatial analysis system that may involve stimulation in a complex fashion yet to be described. This system may involve a combination of volley and spatial mechanisms using both following of the stimulating frequency, as suggested by Furukawa & Ishii (1967), and a discrete place-type mechanism. While it is not reasonable to speculate further on the modes of function of the goldfish ear based on our data, we can suggest that this ear is a co~iderably less complex mechanism than the mammalian cochlea. There does not appear to be the same complex response to temporary threshold shift as in mammals and, further, this type of data does not indicate that there is any great degree of spatial resolution, again as found for some "ITS in l~.mmals. Still needed, however, are detailed investigations of the in-

The auditory system of the goldfish ner ear using physiological and behavioral teehmques as well as modern observational methods for us to gain the precise information on the functioning of the teleost ear A final point to be made is the generality of this system to other ostariophysines and to non-ostariophysines. It is likely that a similar system for acoustic processing ,s functioning in other ostariophysines since both behavioral (Popper, 1972; Popper & Fay, 1973) and physiological (Fay & Popper, 1974, 1975) data suggest significant similarities in audition between diverse ostariophysines. However, generalization to non-ostariophysines is considerably more dillcult since behavioral data and at least certain physiological data differ significantly between the ostariophysines and non-ostanophysmes (Popper & Fay, 1973; Fay & Popper, 1975; Tavolga, 1974). In addition, there are a number of significant morphological differences between the ostariophysine and non-ostariophysine ears including the fact that the saccular otolith in Ostariophysi is very small and has extensive fluting, while m non-ostar~ophysmes it tends to be significantly larger and without fluting. Consequently, there may be a difference in the way m which the differential motion between hair cells and otolith functions in the two groups of animals. While this would not disallow the presence of frequency discriminat~on or even masking in non-ostariophysines (indeed, both have been demonstrated, Dijkgraaf & Verheijen, 1950; Buerkle, 1968; Tavolga, 1974) it might preclude other aspects of audition such as critical-band type mechanism, lack of which has already been demonstrated by Tavolga (1974). It remains for further experiments to determine whether a signal discrlmmahon system in the sensory macula actually exists, SUMMARY Behaworal investigations were made of the effects of intense pure tone stimulation on auditory thresholds for the goldfish (Carassius auratus). Results indicate that different stimulation frequencies have a different effect on the test frequencies while each of the test frequencies had the same degree of threshold shift stimulation to eactI of the stimulation frequencies. Results are interpreted to indicate that the teleost inner ear responds m a relatively complex fashion to different stimulating frequencies and this may indicate some degree of spatial s~gnal analys~s in the inner err. Acknowledgements---This work was supported by Public Health Service grant NS-09374 from the National Institute of Neurological Diseases and Stroke. We thank Robert Moeng and Dr. Inn Cooke for critically reading the manuscript. REFERENCES Bmqrrz L. D., ELDRIDGE D. H. & TEMPLER J W (1972) Temporary threshold slur in Chinchilla: electrophysiological correlates. J. acoustic Soc. Am. $2, 1115-1123. BERG~nK W. A. VAN (1967a) In discussion, Marine Bioacoustics (Edited by TAVOLOAW. N.), VOI. 2, pp. 244. Pergamon Press, New York Br~G~ug W A VA~ (1967b) The evolution of vertebrate hearing. In Contributions to Sensory Physiology (Echted by Nl~'r W. D.), Vol. 2, pp. 1--49. Academic Press, New York. c ,a,P. S3/1A--n

17

BUERKL8 U. (1968) Relation of pure tone thresholds to background noise level in the Atlantac cod (Gadus mothun). J. Fish. Res. Bd Can. 25, 1155-1160 C~r~ P. H., SmEg W. N. & AuwAg~g A, (1970) Acousticlateralis system of fishes: cross-modal coupling of signat and no,se in the grunt, Haeraulon parras. J. account. Soe. Am. 49, 591-594. DAVLSH., B~SON R. W, COVL~ W. P., FERN~NDI~ C., GOLDS~ R., KArSUKtY., LEOOUIXL. P, McAWLWl~ D R. & TASAKtI. (1953) Acoustic trauma in the guinea pig. J. acoust. Soc. Am. 51, 552-558. DUKORA.~ S. & VZRHEU~ F. J. (1950) Neue Versuche tiber des TonunterszheidungsvermiSgen des Elritze. Z. petal. Physiol. 32, 248-256. ELIOT E. N. & F~SER W. (1970) Fatigue and adaptation. In Foundations of Modern Auditory Theory (Edited by TOBt~kSJ. V.), Vol. 1, pp. 115-156, Academic Press, New York.

ENOER P. S (1963) Unit activity m the fish auditory system. Acta physiol, scand. Suppl 59, 1-48 ENGER P. S. (1973) Masking of auditory responses in the medulla oblongata of goldfish. J. exp. Biol. 59, 415--424. FAY R. R. (1969) Behavioral audiogram for the goldfish. J Aud. Res. 9. 112-121. FAY R R. (1970) Auditory frequency discrimination in the goldfish (Carassius auratus). J. eomp. Physiol. Psych. 73, 175--180. FAY R. R. & POPPER A. N. (1974) Acoustic stimulation of the ear of the goldfish. J. exp. B~ol. 61,243-260. FAY R. R & POPPER A. N. (1975) Modes of stimulation of the teleost car. J. exp Biol 62, 379-388.

FuRogxwx T. & ISHnY. (1967) Neurophysiological studies on hearing in goldfish. J. Neurophysiol. 30, 1377-1403. GR0ZZlN~-R B. (I967) Elektro-physiologische Untersuehungen an der Horben der Schleie (Tinca linen L). Z. vergL Physiol 57, 44--76. HUr~R-DUvAn I. M. & ELiOt D. N. (1972) Effects of mtense auditory stimulation Hearing losses and inner ear changes in the squirrel monkey. J acoust Soc Am. 52, 1181-1192. J^coas D. W, & TAVOLGAW N. (1967) Acoustic intensity limens in the goldfish. Anma. Behav. 15, 324--335. JACOaSD. W. & TAVOLOAW. N. (1968) Acoustic frequency discrimination in the goldfish. Anita. Behav. 16, 67-91. KnA~qNA S. M. & TONNDO~ J. (1972) Tympanic membrane vibrations in cats studied by time-averaged holography. J. acoustic Soc. Am. 51, 1904-1920, Low~-Nsrrn~ O. (1971) The labyrinth. In Fish Physiology (Edited by HOAR W. S. & R-~NDALLD. J.), VO1. 5, pp. 207-240 Academic Press, New York. MICrtELS~SA. (1971) The physiology of the locust ear~II Frequency discrimination based upon resonances in the tympanum, Z, vergl, Physiol, 71, 63-101. PAGE C. H. (1970) Electrophysiologieal studies of auditory responses m the goldfish braan, d. Neurophysiol. 35, 116127 POCHE L. B., S1OCKWEU_C. W. & AD~S I4. W. (1969) Cochlear hair-cell damage in guinea pigs after exposure to impulse noise. J. acoust. $oc. Am. 46, 947-951. POPPF.X A. N. (1970) Auditory ~pacitaes of the Mexican blind cave fish Astyanax jordani and its eyed ancestor Astyanax raexicanus. Anita. Behav. lg, 552-562. POPPER A. N. (1971) The effects of size on the auditory capacities of the goldfish. J. Aud. Res. 11, 239-247. Poppr_a A. N. (1972) Pure-tone auditory t~esholds for the carp, Cyprmus carpto. J. aeaust, $oc, Am. 52, 1714--1717. POPPER A. N. (1974) The response of the swim bladder of the goldfish (Carassius auratus) to acoustic stimuli. J exp. Biol. 60, 295-304. POPFER A. N., Cru~ A. T. H. & ~ N. L. (1973) An evaluation of methods for behavioral investigations of teleost audition. Behav. Res. Meth. Instr. 5, 502-503. POPPER A. N. & FAY R. R. (1973) Sound detection and

18

ARTHUR N. Poppt~p. AND NANCY L. CLXRKC

processing by fish: a critical review. J. acoust. Soc. Am. 53, 1515-1529. PRICI~G. R. (1972) FuncUonal changes m the ear produced by high-intenmty sound--II. 500-Hz stamulation. J. acoust. Soc. Am. 51, 552-558 S ~ D O. (1974) Direztional sensitivity of microphonic potentials from the perch ear. J. exp. Biol. 60, 881-899. SELTm~ W. (1964) Adaptation and fatigue. J. acoust. Soc. Am. 36, 2202-2209. S~t~tl~x H. (1929) Untersuchungen uber den Geh/Srsmn der Fische, besondcrs yon Phoxinus laevis L. und Amiurus nebulosus Raf. Z. vergl. Physiol. 9, 339-477 TAVOLGA W. N (1967) Masked auditory thresholds m teleost fishes. In Marine Bio-acoustics (Edited by TAVOLGAW. N.), Vol. 2, pp. 233-245. Pergamon Press, Oxford. TAVOLGA W. N. (1971) Sound production and detection.

In Fish Physiology (Edited by HOAR W. S. & RANDALL D. J.), Vol. 5, pp. 135-205. Academic Press, New York. TAVOLOAW. N. (1974) Signal/noise ratio and critical band In fishes. J aeoust. Soc. Am. 55, 1323-1333. WARD W D. (1953) Auditory fatigue and masking. In Modern Developmems in Audiology (Edited by J~RG~R J.), pp. 240-286 Academic Press, New York. WEVEP, E. G. & LAWRENCE M. (1955) Patterns of injury produced by over-stimulatmn of the ear. J. acoust Soc. Am. 27, 853-858. WOODWARDW. A. (1972) A logarithmic electronic integrator for acuv~ty transducers. Behav. Res Meth Instr. 4, 149-150. Yours(; E. & SACHS M. B. (1973) Recovery from sound exposure in auditory-nerve fibers. J. acoust. Soc Am. 54, 1535-1543.