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Effect of contingent auditory stimuli on concurrent schedule performance: An alternative punisher to electric shock
Available online at www.sciencedirect.com
Behavioural Processes 78 (2008) 421–428
Effect of contingent auditory stimuli on concurrent schedule performance: An alternative punisher to electric shock Phil Reed a,∗ , Toshihiko Yoshino b a
Department of Psychology, Swansea University, Singleton Park, Swansea SA2 8PP, UK b Kobe Shinwa Women’s University, Japan
Received 1 April 2007; received in revised form 11 February 2008; accepted 22 February 2008
Abstract This study explored whether load auditory stimuli could be used as functional punishing stimuli in place of electric shock. Three experiments examined the effect of a loud auditory stimulus on rats’ responding maintained by a concurrent reinforcement schedule. In Experiment 1, overall response rate decreased when a concurrent 1.5 s tone presentation schedule was superimposed on the concurrent variable interval (VI) 180-s, VI 180-s reinforcement schedule. On the contrary, response rate increased when a click presentation schedule was added. In Experiment 2, the extent of the response suppression with a 1.5 s tone presentation varied as a function of the frequency of the reinforcement schedule maintaining responses; the leaner the schedule employed, the greater the response suppression. In Experiment 3, response suppression was observed to be inversely related to the duration of the tone; response facilitation was observed when a 3.0-s tone was used. In Experiments 1 and 2, a preference shift towards the alternative with richer reinforcement was observed when the tone schedule was added. In contrast, the preference shifted towards the leaner alternative when the click or longer duration stimulus was used. These results imply that both the type and duration of a loud auditory stimulus, as well as the reinforcement schedule maintaining responses, have a critical role in determining the effect of the stimuli on responding. They also suggest that a loud auditory stimulus can be used as a positive punisher in a choice situation for rats, when the duration of the tone is brief, and the reinforcement schedule maintaining responses is lean. © 2008 Elsevier B.V. All rights reserved. Keywords: Punishment; Auditory stimuli; Concurrent schedule; Matching law; Choice; Rat
A decade ago, Pierce and Epling (1995) noted a decline in the study of aversively controlled behavior, which has continued over the intervening period. They attributed this relative lack of research into aversively controlled behavior to ethical qualms about the use of electric shock. Thus, finding an acceptable alternative to shock may facilitate study of this area. One possibility that has been suggested concerns the use of auditory cues, which appear to have a suppressive effect on rats’ behavior (e.g., Reed and Yoshino, 2001, 2005). In support of this suggestion, several experiments have demonstrated that a tone stimulus may have aversive properties similar to those of an electric shock. For example, McAdie et al. (1996) found a response bias away from key that produced a 100 dB[A] sound, and toward a key that terminated the sound. Moreover, McAdie et al. (1993) reported that the type of sound used, independently from its intensity, differentially
∗
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affected the extent of this response bias. Similarly, Reed et al. (1995, 1996) showed that a loud tone suppressed lever pressing under an extinction schedule in rats, but that a click facilitated responding. In contrast to the above reports that show some auditory stimuli have suppressive effects on behavior, there are several other studies that do not report such an effect. Symmes and Leaton (1962) and Andronico and Forgays (1962) compared rats’ response rates on a continuous reinforcement schedule with and without response-contingent tone presentations. The former condition produced higher response rates than the latter. However, it should be noted that the intensity of tone they employed was not as loud as that employed in several of the above studies (McAdie et al., 1996; Reed et al., 1995). Thus, before it can be concluded that loud auditory stimuli have aversive properties similar to those of electric shock, the effect of a range of auditory stimuli on behavior needs to be clarified. A number of procedural aspects of the previous studies may have been responsible for producing the differing results. Firstly, the type of auditory stimulus employed may determine its effect
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on responding. Both Reed et al. (1995), and McAdie et al. (1993), showed that the effect of the auditory stimulus depends on its nature independent of its intensity; tones seem to produce suppression whereas clicks produce facilitation. The mechanisms underlying this effect are not clear, but clearly need to be addressed. Secondly, the schedule that maintains responding may have a critical role in determining the impact of the auditory stimulus on responding. Reed et al. (1995) showed that a tone suppressed responding during extinction, whereas, Andronico and Forgays (1962) reported a facilitative effect of tone on the responses under a continuous reinforcement schedule. It may well be that such auditory stimuli are only mildly aversive (relative to electric shock) and their effects are only revealed when the maintaining reinforcement schedule is lean. This suggestion seems to be borne out by the results reported by Reed and Yoshino (2001) from a study of acquisition of leverpress responding in rats. In this study, a brief tone suppressed responding during initial training of a lever-press response, but only when the reinforcement schedules maintaining responding were lean. Thirdly, the duration of a tone appears important in determining the impact on responding. Reed et al. (1995, 1996) used a 1.5-s tone, and showed a suppressive effect on responding. Conversely, Andronico and Forgays (1962) employed a procedure in which a tone lasted as long as the rat held down the lever, and found a facilitative effect. It may be that the aversive effect of an auditory cue habituates with its prolonged presentation, but whatever the mechanism, this functional relationship needs to be investigated to determine the boundary conditions of the suppressive effect of a tone. Thus, the present studies were conducted in an attempt to clarify this under researched area, to corroborate what appears apparent about the effects of auditory stimuli from cross-experimental comparison, and to pave the way for the future use of auditory cues in the investigation of aversively motivated behavior. 1. Experiment 1 The first experiment examined the effect of a loud auditory stimulus on responding maintained by a concurrent reinforcement schedule. It examined whether loud tones and loud clicks have different effects on lever pressing in rats (cf. Reed et al., 1995, 1996). 2. Method 2.1. Subjects Twenty experimentally naive, male Lister Hooded rats were used. The subjects were 4–5 months old at the start of training, had a free-feeding body weight range of 330–370 g. The animals were housed in groups of four, with water consistently available in their home cages. They were maintained at 85% of their freefeeding weight throughout the experiment by daily weighing. Should one rat become too heavy or light, they were separated from the others, and fed until their weight adjusted appropriately.
2.2. Apparatus Four identical two-lever operant chambers were used. Each chamber was located in a light- and sound-attenuating case, ventilated by a fan that provided background masking noise (65 dB[A]). A recessed food tray, through which a reinforcer (one 45-mg food pellet) was delivered, was centrally located between the two levers. A speaker (through which either a tone or a click could be delivered) was mounted on the outside of the ceiling of the chamber. The tone was a broad-band, noisy signal (ranging up to 16 kHz) with spectral peaks at 3 kHz (105 dB[A]) and 500 kHz (125 dB[A]), measured approximately 10 cm from the speaker. The click had the same acoustic properties as the tone except that it was modulated to produce a sound every 100-ms (i.e. it had an on/off cycle of 100 ms on/100 ms off). 2.3. Procedure Subjects were magazine trained in two sessions of a variable time (VT) 60-s schedule (range 1–120 s). Each session terminated after 30 pellet deliveries. Lever pressing then was shaped in five, 20-min sessions according to a conc. VI 15-s VI 15-s schedule. A 2-s change-over delay (COD) was in operation, such that a response to a particular schedule would not be reinforced if it was made less than 2 s after a response to the alternative schedule. Subjects then received 15, 40-min sessions of a conc. VI 30-s VI 30-s schedule, along with a 2-s COD. Following pre-training, subjects were divided into five experimental groups (n = 4), counterbalanced for response rates, and response allocations (responses to the left lever divided by the total responses), during the last five sessions of conc. VI 30-s VI 30-s. The experimental treatment included seven phases: Baseline sessions 1, Tone sessions 1, Baseline sessions 2, Click sessions, Baseline sessions 3, Tone sessions 2, and Baseline sessions 4. Throughout these phases, each group consistently received either, conc. VI 90-s VI 30-s, conc. VI 60-s VI 30-s, conc. VI 30-s VI 30-s, conc. VI 30-s VI 60-s, or conc. VI 30-s VI 90-s schedules. Baseline sessions 1, comprised 23, 40-min sessions. Each of the following six phases comprised 10, 40-min sessions. During Tone sessions 1 and 2, each group received a conc. VI 60-s VI 60-s schedule of 1.5-s response-contingent tone presentations, superimposed over their reinforcement schedule, with a 2-s COD in operation on this schedule. The intensity of tone was 105 dB[A] in Tone sessions 1, and 125 dB[A] in Tone sessions 2. In Click sessions, each group received a conc. VI 60-s VI 60-s schedule of 1.5-s response-contingent click presentations (105 dB[A]) as well as each reinforcement schedule, with a 2-s COD. 2.4. Data collection and analyses During each Baseline session, the number of responses for each lever, the number of reinforcers for pressing each lever, and the accumulated time spent on each lever (i.e. the accumulated inter-response time including changeover delays), were recorded. This was measured as the time from the first response
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on one lever to the first response on the other lever. During the Tone and Click phases, the number of tone or click presentations for each lever were also counted. The data from the last five sessions in each phase were used to calculate group means for these measures. These data from the seven phases were collapsed to allow three comparisons. Each of these stages consisted of Baseline and Intervention (i.e. Tone or Click) sessions. “Stage 1” refers to the averaged data from the Baseline sessions 1 and 2 versus the Tone sessions 1. “Stage 2” refers to those from the Baseline sessions 2 and 3 versus the Click sessions. “Stage 3” refers to those from the Baseline 3 and 4 versus the Tone sessions 2. The averaged data were described in terms of responses, time spent responding (s), reinforcement (per min), and tone or click presentations (per min). A least squares linear regression analysis described a regression line for each condition in each Stage, for response allocation. The log of the ratio of response rates for each component were described as a function of the log of the ratio of the reinforcer rate for each condition in each stage. Eq. (1) (Baum, 1974; Davison and McCarthy, 1988; p.49) was used for this linear regression analysis: B1 R1 log = a ∗ log + log c (1) B2 R2 where B1 and B2 denote response rates, and R1 and R2 denote obtained reinforcement rates for the left and right lever, respectively. 3. Results and discussion Fig. 1 shows group-mean response rates for each condition across the two alternatives, in each stage by reinforcement schedule. The main effect of condition is shown more clearly in the averaged response rates across schedules (Fig. 2). Inspection of Fig. 1 shows that throughout all stages, rats responding on the conc. VI 30-s VI 60-s schedule showed the highest response rate, rats under conc. VI 30-s VI 90-s, except during Tone in Stage 3, came next, followed by those under conc. VI 30-s VI
Fig. 1. Overall response rates over the last 5 sessions of each stage, each condition, for each group. BASE = Baseline sessions, TONE = Tone sessions, CLICK = Click sessions.
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Fig. 2. Overall response rates over the last 5 sessions averaged across groups for each stage and each condition. Error bars display the standard errors of mean. Stage 1 and Stage 3 consisted of the Baseline sessions and the Tone sessions, and Stage 2 consisted of the Baseline sessions and the Click sessions.
30-s, conc. VI 60-s VI 30-s, and conc. VI 90-s VI 30-s, respectively. Figs. 1 and 2 both show that group-mean response rates in Stage 2, generally, were higher than those in either Stage 1 or 3. Fig. 2 shows that response rates during the Tone condition, both in Stages 1 and 3, were lower than those during the appropriate Baseline sessions, whereas those during Click condition were generally higher than those during the Baseline phase. A three-way analysis of variance (ANOVA) was conducted on these response rate data with reinforcement schedule (Schedule) as a between-subject factor, and Stage (1–3), and Condition (Baseline/Tone or Click), as within-subject factors. A rejection criterion of p < .05 was adopted for this, and all subsequent analyses. The ANOVA revealed significant main effects of Schedule, F(4,15) = 4.68, and Stage, F(2,30) = 10.33. The interactions between Stage and Condition, F(2,30) = 13.43, and between Condition and Schedule, F(4,15) = 3.67, were also significant. Neither the other main effect, nor the other interactions, proved to be statistically significant (all ps > .10). As both interactions including the Condition (baseline versus auditory stimulus) factor were significant, further two-way ANOVA (Schedule × Condition) were conducted for each stage, with the appropriate corrections for the degrees of freedom (Howell, 1992, p.449). The main effect of Condition was significant in all stages. In both Stage 1 (F(1,15) = 14.82), and Stage 3 (F(1,15) = 6.48), the baseline condition produced a higher rate than the Tone condition; whereas in Stage 2 (F(1,15) = 9.43) the click condition produced a higher rate than the baseline condition. The main effect of Schedule was significant in Stage 1, F(4,15) = 5.38, and Stage 2, F(4,15) = 4.59, but not in Stage 3, F(4,15) = 2.53. The interaction of these two factors was not significant in any of the Stages, ps > .05. Table 1 displays the results of the least square linear regression analyses. Although based on a small number of points and, hence, only tentative, three consistent tendencies were found in these regressions. First, all regressions fitted well to each set of data (all VACs > 95%). All slope values were lower than 0.8 indicating that under-matching occurred. The intercepts generally were larger than zero, indicating a response bias to the left lever. Finally, the slope values revealed the reinforcer sensitivity
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Table 1 Log response ratios (y) as a function of log obtained reinforcer ratios (x), in each stage, and each condition of Experiment 1 Response allocation Stage 1 Baseline Stage 1 Tone Stage 2 Baseline Stage 2 Click Stage 3 Baseline Stage 3 Tone 2
y = 0.061 + 0.638x (VAC = 95.6%) y = 0.051 + 0.741x (VAC = 99.3%) y = 0.051 + 0.598x (VAC = 99.5%) y = 0.037 + 0.519x (VAC = 95.8%) y = 0.062 + 0.587x (VAC = 99.5%) y = 0.063 + 0.670x (VAC = 98.3%)
All data shown were the average over the last 5 sessions in each group. Equations for the regression analyses are given with the variances accounted for in parentheses.
during Tone was higher than that during its baseline, whereas the slope value during Click was lower than that during its baseline. In summary these data show that the tone and click stimuli had different effects on responding: a loud tone suppressed, and a click facilitated, responding. These data suggest that the type of an auditory stimulus may be important in determining its effect on responding, in addition to its intensity (see also McAdie et al., 1993). They also support previous demonstrations of the effects of tones and clicks on rats’ behavior (Reed et al., 1995); the former stimulus suppressed behavior, whereas the latter stimulus facilitated responding. Thus, to the extent that the tone served to suppress responding and enhance sensitivity to reinforcement (as indexed by the shift in the matching behavior of the rats) it appears to function in a similar manner to an electric shock. 4. Experiment 2 It should be noted that the extent of the suppressive effect of a tone in Experiment 1 was not large. Certainly, it might be expected that responding would be suppressed to a greater degree by the superimposition of a foot shock. If a tone could be employed in this context to facilitate research into aversive control of behavior, it would be helpful if a stronger effect could be noted. Reed et al. (1995, 1996) found a large suppressive effect when the tone was presented during extinction. In the present Experiment 1, however, the tone was introduced on relatively rich reinforcement schedules. As noted in the General introduction, the suppressive effect of a response-contingent tone may be stronger on leaner schedules (see also Reed and Yoshino, 2001). Experiment 2 was designed to investigate whether the suppressive effect of a loud tone varies as a function of the reinforcement schedule. That is, does a larger suppressive effect occur under a lean reinforcement schedule after extended training. 5. Method 5.1. Subjects and apparatus Sixteen experimentally naive, male Lister Hooded rats served. The subjects were 7–8 months old at the start of training, had a free-feeding body weight range of 445–595 g. Other details regarding subjects and apparatus were as described in Experiment 1.
5.2. Procedure The first two stages of two magazine training sessions were identical to those in Experiment 1. Following this, subjects were divided into four experimental groups (n = 4) counterbalanced for response rates to the two levers, and for the response allocations on the basis of the last three sessions of the conc. VI 15-s VI 15-s schedule. Subjects then received further pre-training. Throughout these stages each group consistently received a relative reinforcement allocation of 3:1, 2:1, 1:2, or 1:3 on the two levers. The schedules for each group in each stage are summarized in Table 2. Each session lasted 40-min, and a 2-s COD was in effect. The experimental treatment included four stages, each consisting of eight Baseline sessions, eight Tone sessions, and five Recovery sessions. The reinforcement schedules for each group in each stage also are summarized in Table 2. During the Tone sessions, each group received a conc. VI 60-s VI 60-s schedule of tone presentation along with each reinforcement schedule. The intensity of the tone was 105 dB[A] and its length was 1.5s throughout the stages. Each session lasted 40-min, and a 2-s COD applied to both the reinforcement schedule and tone presentation schedule. The Tone sessions were followed by five Recovery sessions, during which each group received the same reinforcement schedule as in the Baseline sessions prior to the Tone sessions. 5.3. Data collection and analysis Three variables were recorded during the Baseline and Recovery sessions, and four during the Tone sessions, as described in Experiment 1. The data from the last five sessions in the Baseline or Tone sessions, and the last three sessions in the Recovery sessions, were used to calculate group means for these measures. The data from the Baseline and Recovery sessions were combined to obtain a single mean for each stage, and this was compared with that during the Tone sessions. Other aspects of data collection and analyses were as described in Experiment 1. Table 2 Values of variable interval schedules for each alternative employed during pretraining and experimental stages for each group of Experiment 2 Group 3:1
Group 2:1
Group 1:2
Group 1:3
Left
Right
Left
Right
Left
Right
Left
Right
25 50 75 100 125
75 150 225 300 375
25 50 75 100 125
50 100 150 200 250
50 100 150 200 250
25 50 75 100 125
75 150 225 300 375
25 50 75 100 125
Experimental stages 1 (Lean) 150 2 (Rich) 50 3 (Middle) 100 4 (Lean) 150
450 150 300 450
150 50 100 150
300 100 200 300
300 100 200 300
150 50 100 150
450 150 300 450
150 50 100 150
Pretraining 1 2 3 4 5
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6. Results and discussion Figs. 3 and 4 depict the group-mean response rates for each condition, in each stage, for each reinforcement schedule. The main effect of Stage is shown much more clearly in the averaged response rates across the schedules (Fig. 4). In the six of the eight conditions, the 1:3 reinforcement rate group showed the highest rate of responding, and in seven out of eight conditions the 3:1 group showed the lowest. The rates of responding for the other two groups was not consistent across the conditions. Group-mean response rates increased from Stage 1 (lean schedule) to Stage 2 and 3 (rich and middle schedule), and decreased in Stage 4 when the leaner reinforcement schedule was reinstated. The response rates during the Tone phases were lower than those during the Baseline phases. Regardless the reinforcement schedule employed, every group showed lower levels of responding during the tone phases than that during the baseline phases.
Fig. 3. Overall response rates over the last 5 sessions of each stage, each condition, for each group. 3:1, 2:1, 1:2 and 1:3 refer to ratios of reinforcement schedules for left to right lever, which each experimental groups received. LEAN, RICH, and MIDDLE refer to the reinforcement frequency. BASE = Baseline sessions, TONE = Tone sessions. See Table 2 for schedules in detail.
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As the purpose was to examine the suppressive effect of tone as a function of different reinforcement schedules, twoway ANOVAs for the main effects of Schedule and Condition were conducted, with appropriate modifications for the degrees of freedom (Howell, 1992, p.449). These analyses revealed that the main effect of Condition was significant only in Stage 1, F(1,12) = 10.01, and in Stage 4, F(1,12) = 4.32; that is, during the two lean schedule phases. There was no significant effect of condition in either Stages 2 or 3, ps > .10. These analyses showed no significant main effect of Schedule, ps > .50, and no significant interaction, for any Stage, ps > .20. Results of the least square linear regression analyses are summarized in Table 3. Although needing to be treated with some caution, all regression lines fitted to each set of data well (VAC > 94%). The slope values were generally lower than 1.0, suggesting that under-matching occurred. All intercepts were positive and revealed a response bias to the left alternative. Comparisons of the slope values across conditions revealed slope values generally increased on transfer from Baseline to Tone conditions. In the current experiment the tone suppressed responding, and the degree of suppression varied as a function of the reinforcement schedule. There was greater suppression under leaner reinforcement schedules, but little suppression when reinforcement was more frequent. This effect confirms what was apparent from cross-experimental comparison (cf. Andronico and Forgays, 1962; Reed et al., 1995; Reed and Yoshino, 2001). This effect corroborates that noted in Experiment 1, where tones were found to suppress responding, and suggests that in addition to suppressing responding, a tone also alters sensitivity to reinforcement in a similar manner to an electric shock. This second conclusion should be tempered in that the effect of the tone varied, to some extent, with the order of its presentation. The suppressive effect was greatest during Stage 1 (the leanest schedule), and diminished over the next two stages. However, the suppressive effect did emerge again in the response rate data of Stage 4. This would undermine the suggestion that the effect of tone merely reflected an order effect (possibly due to habituation of the effectiveness of the tone across phases). There are two issues that are worthy of some brief mention. It should be noted that the rates of reinforcement for the LEAN Stages in Group 3:1, and in Group 1:3, was actually one third Table 3 Log response ratios (y) as a function of log obtained reinforcer ratios (x), in each stage, and each condition of Experiment 2 Response allocation Stage 1 Baseline Stage 1 Tone Stage 2 Baseline Stage 2 Tone Stage 3 Baseline Stage 3 Tone Stage 4 Baseline Stage 4 Tone
Fig. 4. Overall response rates over the last 5 sessions averaged across groups of each stage and each condition. Error bars display the standard errors of mean. LEAN, RICH, and MIDDLE refer to the reinforcement frequency. See Table 2 for schedules in detail.
y = 0.065 + 0.797x (VAC = 98.9%) y = 0.079 + 0.911x (VAC = 97.4%) y = 0.046 + 0.808x (VAC = 99.6%) y = 0.092 + 0.862x (VAC = 99.7%) y = 0.059 + 0.879x (VAC = 100%) y = 0.062 + 0.924x (VAC = 97.7%) y = 0.048 + 0.805x (VAC = 99.2%) y = 0.028 + 0.857x (VAC = 99.3%)
All data shown were the average over the last 5 sessions in each group. Equations for the regression analyses are given with the variances of accounted for in parentheses.
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greater overall, compared to those rates in that stage for Group 2:1, and Group 1:2 (i.e. 600 vs. 450). Therefore, if the current findings regarding the impact of the density of reinforcement on the effectiveness of the tone as a punisher held, it might be expected that Groups 3:1 and 1:3 would show a less suppression than the two 2:1 groups. Inspection of Fig. 3 shows that, in general, this does seem to hold, although this clearly requires further and more detailed study than is allowed by the numbers of subjects employed in this experiment. Secondly, it may be worth noting that response rates overall were lower in Experiment 2 than in Experiment 1. The reason for this may either be that the rats used in Experiment 2 were older and heavier than those in Experiment 1, or that the schedules employed in Experiment 2 were, in general, leaner than those in Experiment 1. Whatever the reason for this lower rate, it may be the smaller amount of tone-induced suppression found in Experiment 2 was related to this lower response rate (perhaps through the influence of a floor effect). 7. Experiment 3 The third experiment investigated whether the duration of a loud tone affects its suppressive effect. Reed et al. (1995, 1996) used a 1.5-s tone, and showed a suppressive effect of a tone on responding. In contrast, Andronico and Forgays (1962) employed a procedure in which a tone lasted as long as the rat held down the lever, and found a facilitative effect of a tone on responding. To explore this issue, three levels of tone duration were employed to compare the suppressive effects of a tone with such durations to each other. 8. Method 8.1. Subjects and apparatus Twelve experimentally naive, male Lister Hooded rats were used. The subjects were 6 months old at the start of training, had a free-feeding body weight range of 420–490 g. All other details of the subject maintenance, and concerning the apparatus used in this study are as described in Experiment 1.
The Tone sessions were followed by the eight Recovery sessions, during which each group received the same reinforcement schedule as during the Baseline stage. Every session throughout all stages lasted 40-min, and a 2-s COD was effective for both of the reinforcement and tone presentation schedules. 9.1. Data collection and analysis Data concerning three variables were recorded during each session of each Phase as described in Experiment 1. The data from the last four sessions in each stage, and from the first four sessions in the Tone and Recovery sessions, were used to calculate group means for these measures. 10. Results and discussion Fig. 5 depicts the overall group-mean response rate during the last four sessions in each stage. Response rates during Baseline and Recovery were at similar levels among the groups. The response rate during Tone was lower in Group 0.5, and Group 1.0, but the response rate during Tone was higher in Group 3.0. A two-way ANOVA (duration × condition) revealed no main effects, ps > 0.40, but a significant interaction, F(2,4) = 8.27. The simple effect of condition for each group were significant: F(2,6) = 7.75, for Group 0.5; F(2,6) = 5.41, for Group 1.0; and, F(2,6) = 6.40, for Group 3.0. To examine the suppressive effect of the tone, Newman–Keuls’ Tests revealed that the differences between Baseline and Tone, and Tone and Recovery, were significant for Groups 0.5 and 3.0. For Group 1.0, the comparison between Tone and Recovery was significant, but that between Baseline and Tone was not. No significant effect was obtained in the comparison between Baseline and Recovery for any group. These results demonstrate that a short-duration tone produced a suppressive effect, and the long-duration tone produced a facilitative effect, on responding (see also Reed and Yoshino,
9. Procedure Each subject received three pre-training stages as described in Experiment 1. The experimental treatments included three stages: twenty sessions of Baseline, eight sessions of Tone, and eight sessions of Recovery. All rats received a conc. VI 180-s VI 180-s schedule throughout the experimental sessions. After 10 Baseline sessions, the subjects were divided into three experimental groups (n = 4). These groups were counterbalanced for response rates and response allocations during the last 5 of these sessions. During the Tone sessions, each rat received a conc. VI 60-s VI 60-s schedule of tone presentation along with the reinforcement schedule. A 0.5-s tone was employed for rats in Group 0.5; 1.0s for those in Group 1.0; and 3.0-s for those in Group 3.0. The intensity of the tone was 105 dB[A] for all groups.
Fig. 5. Overall response rates over the last 4 sessions of each stage, for each group of tone duration. Error bars display the standard errors of mean. 0.5, 1.0, and 3.0 denote the duration of the tone employed during the Tone sessions for each group (in seconds). BASE = Baseline sessions, TONE = Tone sessions, RECOV = Recovery sessions.
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2001). This provides further evidence of the punishing effect of a tone, establishing that a tone will be suppressive if it is short. Concerning the facilitative effect of 3.0-s tone, three explanations could be considered. Firstly, the hedonic value of the tone may have increased with its duration. Secondly, the longer tone may have facilitated the arousal level of rats. Thirdly, the operation of a coincidental escape contingency may explain the facilitative effect of the tone. Some responses during the tone presentation may have been adventitiously reinforced by the termination of the tone (see Baron, 1991). Although this last assumption appears plausible, it is not clear whether this kind of contingency existed in the current experiment, and additional speculation is not warranted on the basis of the present data. 11. General discussion The present series of studies was designed to confirm the conditions under which an auditory stimulus would serve as a punishing stimulus for operant behavior. This investigation was motivated by the need to find a more acceptable aversive cue than an electric shock, in order to facilitate the investigation of aversively controlled behavior. Also, it was motivated by the issues suggested by cross-experimental comparison of studies of the effects of auditory stimuli on instrumental responding. The current studies demonstrated that both the type, and duration, of a loud auditory stimulus were important in determining its suppressive effect on instrumental responding. Experiment 1 noted that a response-dependent tone, but not a click, suppressed ongoing instrumental responding (see also Reed et al., 1995). Experiment 3 noted that short rather than long stimuli produced a suppressive effect on responding (see also Reed and Yoshino, 2001). That longer duration tones facilitate responding is consistent with previous work (Andronico and Forgays, 1962). In addition, as well as the properties of the auditory stimulus, the value of the reinforcement schedule over which it is superimposed, determine its effect on responding. Experiment 2 demonstrated that the suppression was greatest under leaner schedules of reinforcement (Reed and Yoshino, 2001). Thus, a brief loud tone has a suppressive effect under a lean reinforcement schedule. These results help to explain several of the discrepant findings in the sensory reinforcement literature reported in the general introduction. Moreover, these results demonstrate that an auditory stimulus may serve as a functional punisher for behavioral studies of learning. In addition to the general suppressive effect on responding, the present data show, albeit tentatively, that a tone shifts the preference towards a richer alternative (see Experiments 1 and 2). Studies using an electric shock as a punisher also consistently show such a preference shift (De Villiers, 1980; Farley, 1980). Although the results obtained from these studies do indicate that a loud brief tone can be used as a punisher when the experimental settings are well chosen, the magnitude of the effects observed was quite small. This may result from the use of intermittent punishment schedules in all studies, which is
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typically less pronounced than the effect of punishment applied to every response (see Azrin and Holz, 1966, for a thorough discussion). However, if the effect could be enhanced in future work, then it could offer a more ethically acceptable stimulus through which to study punishment. It should be noted that rats hearing is damaged, by noises loader than 110 dB, only after 5 days constant exposure (Cappaert et al., 2000), and so the current short durations of auditory stimulation should not present such a physical risk to the animals. Given this, the use of auditory stimuli may be a solution to the problem noted by Pierce and Epling (1995, p.241), who note that: “On the basis of animal ethics, investigations of punishment have almost been eliminated at the basic level”. In order to conduct investigations of the effect of punishment, it would be appropriate, and valid, if a loud, short-duration tone was used to punish responses maintained by a relatively lean reinforcement schedule. Acknowledgements These data were collected as part of a thesis, submitted in requirement of a doctorate, by the second author, at University College London. Thanks are due to Lisa A. Osborne and Andy Lattal for their support and comments. Correspondence concerning this article should be addressed to: Phil Reed, Department of Psychology, Swansea University, Singleton Park, Swansea, SA2 8PP, U.K. (e-mail: [email protected]). References Andronico, M.P., Forgays, D.G., 1962. Sensory stimulation and secondary reinforcement. The Journal of Psychology 54, 209–219. Azrin, N.H., Holz, W.C., 1966. Punishment. In: Honig, W.K. (Ed.), Operant Behavior: Areas of Research and Application. Appleton-Century-Crofts, New York, pp. 380–447. Baron, A., 1991. Avoidance and punishment. In: Iversen, I.H., Lattal, K.A. (Eds.), Experimental Analysis of Behavior (Part1). Elsevier Science Publishers, Amsterdam, pp. 173–217. Baum, W.M., 1974. On two types of deviation from the matching law: Bias and undermatching. Journal of the Experimental Analysis of Behavior 22, 231–242. Cappaert, N.L.M., Klis, S.F.L., Muijser, H., Kulig, B.M., Smoorenburg, G.F., 2000. Noise induced hearing loss in rats. Noise and Health 3, 23–32. Davison, M., McCarthy, D., 1988. The Matching Law: A Research Review. Lawrence Earlbaum, Hillsdale, NJ. De Villiers, P.A., 1980. Toward a quantitative theory of punishment. Journal of the Experimental Analysis of Behavior 33, 15–25. Farley, J., 1980. Reinforcement and punishment effects in concurrent schedules: a test of two models. Journal of the Experimental Analysis of Behavior 33, 311–326. Howell, D.C., 1992. Statistical Methods for Psychology, 2nd Ed. PWS-Kent Publishing, Boston, MA. McAdie, T.M., Foster, R.M., Temple, W., 1996. Concurrent schedules: qualifying the aversiveness of noise. Journal of the Experimental Analysis of Behavior 65, 37–55. McAdie, T.M., Foster, R.M., Temple, W., Matthews, L.R., 1993. A method for measuring the aversiveness of sounds to domestic hens. Applied Animal Behaviour Science 27, 223–238. Pierce, W.D., Epling, W.F., 1995. Behavior analysis and learning. Prentice Hall, Englewood Cliffs, NJ. Reed, P., Collinson, T., Nokes, T., 1995. Aversive properties of auditory stimuli. Learning and Motivation 26, 101–115.
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Reed, P., Mitchel, C., Nokes, T., 1996. Intrinsic reinforcing properties of putatively neutral stimuli in an instrumental two-levers discrimination task. Animal Learning & Behavior 24, 38–45. Reed, P., Yoshino, T., 2001. The effect of response-dependent tones on the acquisition of concurrent behavior in rats. Learning and Motivation 32, 255–273.
Reed, P., Yoshino, T., 2005. Effects of contingent tone on concurrent schedule performance at different deprivation levels. European Journal of Behaviour Analysis, 6. Symmes, D., Leaton, R.N., 1962. Failure to observe reinforcing properties of sound onset in rats. Psychological Reports 10, 458.
Behavioural Processes 78 (2008) 421–428
Effect of contingent auditory stimuli on concurrent schedule performance: An alternative punisher to electric shock Phil Reed a,∗ , Toshihiko Yoshino b a
Department of Psychology, Swansea University, Singleton Park, Swansea SA2 8PP, UK b Kobe Shinwa Women’s University, Japan
Received 1 April 2007; received in revised form 11 February 2008; accepted 22 February 2008
Abstract This study explored whether load auditory stimuli could be used as functional punishing stimuli in place of electric shock. Three experiments examined the effect of a loud auditory stimulus on rats’ responding maintained by a concurrent reinforcement schedule. In Experiment 1, overall response rate decreased when a concurrent 1.5 s tone presentation schedule was superimposed on the concurrent variable interval (VI) 180-s, VI 180-s reinforcement schedule. On the contrary, response rate increased when a click presentation schedule was added. In Experiment 2, the extent of the response suppression with a 1.5 s tone presentation varied as a function of the frequency of the reinforcement schedule maintaining responses; the leaner the schedule employed, the greater the response suppression. In Experiment 3, response suppression was observed to be inversely related to the duration of the tone; response facilitation was observed when a 3.0-s tone was used. In Experiments 1 and 2, a preference shift towards the alternative with richer reinforcement was observed when the tone schedule was added. In contrast, the preference shifted towards the leaner alternative when the click or longer duration stimulus was used. These results imply that both the type and duration of a loud auditory stimulus, as well as the reinforcement schedule maintaining responses, have a critical role in determining the effect of the stimuli on responding. They also suggest that a loud auditory stimulus can be used as a positive punisher in a choice situation for rats, when the duration of the tone is brief, and the reinforcement schedule maintaining responses is lean. © 2008 Elsevier B.V. All rights reserved. Keywords: Punishment; Auditory stimuli; Concurrent schedule; Matching law; Choice; Rat
A decade ago, Pierce and Epling (1995) noted a decline in the study of aversively controlled behavior, which has continued over the intervening period. They attributed this relative lack of research into aversively controlled behavior to ethical qualms about the use of electric shock. Thus, finding an acceptable alternative to shock may facilitate study of this area. One possibility that has been suggested concerns the use of auditory cues, which appear to have a suppressive effect on rats’ behavior (e.g., Reed and Yoshino, 2001, 2005). In support of this suggestion, several experiments have demonstrated that a tone stimulus may have aversive properties similar to those of an electric shock. For example, McAdie et al. (1996) found a response bias away from key that produced a 100 dB[A] sound, and toward a key that terminated the sound. Moreover, McAdie et al. (1993) reported that the type of sound used, independently from its intensity, differentially
∗
Corresponding author. Tel.: +44 1792 602047. E-mail address: [email protected] (P. Reed).
0376-6357/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.beproc.2008.02.013
affected the extent of this response bias. Similarly, Reed et al. (1995, 1996) showed that a loud tone suppressed lever pressing under an extinction schedule in rats, but that a click facilitated responding. In contrast to the above reports that show some auditory stimuli have suppressive effects on behavior, there are several other studies that do not report such an effect. Symmes and Leaton (1962) and Andronico and Forgays (1962) compared rats’ response rates on a continuous reinforcement schedule with and without response-contingent tone presentations. The former condition produced higher response rates than the latter. However, it should be noted that the intensity of tone they employed was not as loud as that employed in several of the above studies (McAdie et al., 1996; Reed et al., 1995). Thus, before it can be concluded that loud auditory stimuli have aversive properties similar to those of electric shock, the effect of a range of auditory stimuli on behavior needs to be clarified. A number of procedural aspects of the previous studies may have been responsible for producing the differing results. Firstly, the type of auditory stimulus employed may determine its effect
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on responding. Both Reed et al. (1995), and McAdie et al. (1993), showed that the effect of the auditory stimulus depends on its nature independent of its intensity; tones seem to produce suppression whereas clicks produce facilitation. The mechanisms underlying this effect are not clear, but clearly need to be addressed. Secondly, the schedule that maintains responding may have a critical role in determining the impact of the auditory stimulus on responding. Reed et al. (1995) showed that a tone suppressed responding during extinction, whereas, Andronico and Forgays (1962) reported a facilitative effect of tone on the responses under a continuous reinforcement schedule. It may well be that such auditory stimuli are only mildly aversive (relative to electric shock) and their effects are only revealed when the maintaining reinforcement schedule is lean. This suggestion seems to be borne out by the results reported by Reed and Yoshino (2001) from a study of acquisition of leverpress responding in rats. In this study, a brief tone suppressed responding during initial training of a lever-press response, but only when the reinforcement schedules maintaining responding were lean. Thirdly, the duration of a tone appears important in determining the impact on responding. Reed et al. (1995, 1996) used a 1.5-s tone, and showed a suppressive effect on responding. Conversely, Andronico and Forgays (1962) employed a procedure in which a tone lasted as long as the rat held down the lever, and found a facilitative effect. It may be that the aversive effect of an auditory cue habituates with its prolonged presentation, but whatever the mechanism, this functional relationship needs to be investigated to determine the boundary conditions of the suppressive effect of a tone. Thus, the present studies were conducted in an attempt to clarify this under researched area, to corroborate what appears apparent about the effects of auditory stimuli from cross-experimental comparison, and to pave the way for the future use of auditory cues in the investigation of aversively motivated behavior. 1. Experiment 1 The first experiment examined the effect of a loud auditory stimulus on responding maintained by a concurrent reinforcement schedule. It examined whether loud tones and loud clicks have different effects on lever pressing in rats (cf. Reed et al., 1995, 1996). 2. Method 2.1. Subjects Twenty experimentally naive, male Lister Hooded rats were used. The subjects were 4–5 months old at the start of training, had a free-feeding body weight range of 330–370 g. The animals were housed in groups of four, with water consistently available in their home cages. They were maintained at 85% of their freefeeding weight throughout the experiment by daily weighing. Should one rat become too heavy or light, they were separated from the others, and fed until their weight adjusted appropriately.
2.2. Apparatus Four identical two-lever operant chambers were used. Each chamber was located in a light- and sound-attenuating case, ventilated by a fan that provided background masking noise (65 dB[A]). A recessed food tray, through which a reinforcer (one 45-mg food pellet) was delivered, was centrally located between the two levers. A speaker (through which either a tone or a click could be delivered) was mounted on the outside of the ceiling of the chamber. The tone was a broad-band, noisy signal (ranging up to 16 kHz) with spectral peaks at 3 kHz (105 dB[A]) and 500 kHz (125 dB[A]), measured approximately 10 cm from the speaker. The click had the same acoustic properties as the tone except that it was modulated to produce a sound every 100-ms (i.e. it had an on/off cycle of 100 ms on/100 ms off). 2.3. Procedure Subjects were magazine trained in two sessions of a variable time (VT) 60-s schedule (range 1–120 s). Each session terminated after 30 pellet deliveries. Lever pressing then was shaped in five, 20-min sessions according to a conc. VI 15-s VI 15-s schedule. A 2-s change-over delay (COD) was in operation, such that a response to a particular schedule would not be reinforced if it was made less than 2 s after a response to the alternative schedule. Subjects then received 15, 40-min sessions of a conc. VI 30-s VI 30-s schedule, along with a 2-s COD. Following pre-training, subjects were divided into five experimental groups (n = 4), counterbalanced for response rates, and response allocations (responses to the left lever divided by the total responses), during the last five sessions of conc. VI 30-s VI 30-s. The experimental treatment included seven phases: Baseline sessions 1, Tone sessions 1, Baseline sessions 2, Click sessions, Baseline sessions 3, Tone sessions 2, and Baseline sessions 4. Throughout these phases, each group consistently received either, conc. VI 90-s VI 30-s, conc. VI 60-s VI 30-s, conc. VI 30-s VI 30-s, conc. VI 30-s VI 60-s, or conc. VI 30-s VI 90-s schedules. Baseline sessions 1, comprised 23, 40-min sessions. Each of the following six phases comprised 10, 40-min sessions. During Tone sessions 1 and 2, each group received a conc. VI 60-s VI 60-s schedule of 1.5-s response-contingent tone presentations, superimposed over their reinforcement schedule, with a 2-s COD in operation on this schedule. The intensity of tone was 105 dB[A] in Tone sessions 1, and 125 dB[A] in Tone sessions 2. In Click sessions, each group received a conc. VI 60-s VI 60-s schedule of 1.5-s response-contingent click presentations (105 dB[A]) as well as each reinforcement schedule, with a 2-s COD. 2.4. Data collection and analyses During each Baseline session, the number of responses for each lever, the number of reinforcers for pressing each lever, and the accumulated time spent on each lever (i.e. the accumulated inter-response time including changeover delays), were recorded. This was measured as the time from the first response
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on one lever to the first response on the other lever. During the Tone and Click phases, the number of tone or click presentations for each lever were also counted. The data from the last five sessions in each phase were used to calculate group means for these measures. These data from the seven phases were collapsed to allow three comparisons. Each of these stages consisted of Baseline and Intervention (i.e. Tone or Click) sessions. “Stage 1” refers to the averaged data from the Baseline sessions 1 and 2 versus the Tone sessions 1. “Stage 2” refers to those from the Baseline sessions 2 and 3 versus the Click sessions. “Stage 3” refers to those from the Baseline 3 and 4 versus the Tone sessions 2. The averaged data were described in terms of responses, time spent responding (s), reinforcement (per min), and tone or click presentations (per min). A least squares linear regression analysis described a regression line for each condition in each Stage, for response allocation. The log of the ratio of response rates for each component were described as a function of the log of the ratio of the reinforcer rate for each condition in each stage. Eq. (1) (Baum, 1974; Davison and McCarthy, 1988; p.49) was used for this linear regression analysis: B1 R1 log = a ∗ log + log c (1) B2 R2 where B1 and B2 denote response rates, and R1 and R2 denote obtained reinforcement rates for the left and right lever, respectively. 3. Results and discussion Fig. 1 shows group-mean response rates for each condition across the two alternatives, in each stage by reinforcement schedule. The main effect of condition is shown more clearly in the averaged response rates across schedules (Fig. 2). Inspection of Fig. 1 shows that throughout all stages, rats responding on the conc. VI 30-s VI 60-s schedule showed the highest response rate, rats under conc. VI 30-s VI 90-s, except during Tone in Stage 3, came next, followed by those under conc. VI 30-s VI
Fig. 1. Overall response rates over the last 5 sessions of each stage, each condition, for each group. BASE = Baseline sessions, TONE = Tone sessions, CLICK = Click sessions.
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Fig. 2. Overall response rates over the last 5 sessions averaged across groups for each stage and each condition. Error bars display the standard errors of mean. Stage 1 and Stage 3 consisted of the Baseline sessions and the Tone sessions, and Stage 2 consisted of the Baseline sessions and the Click sessions.
30-s, conc. VI 60-s VI 30-s, and conc. VI 90-s VI 30-s, respectively. Figs. 1 and 2 both show that group-mean response rates in Stage 2, generally, were higher than those in either Stage 1 or 3. Fig. 2 shows that response rates during the Tone condition, both in Stages 1 and 3, were lower than those during the appropriate Baseline sessions, whereas those during Click condition were generally higher than those during the Baseline phase. A three-way analysis of variance (ANOVA) was conducted on these response rate data with reinforcement schedule (Schedule) as a between-subject factor, and Stage (1–3), and Condition (Baseline/Tone or Click), as within-subject factors. A rejection criterion of p < .05 was adopted for this, and all subsequent analyses. The ANOVA revealed significant main effects of Schedule, F(4,15) = 4.68, and Stage, F(2,30) = 10.33. The interactions between Stage and Condition, F(2,30) = 13.43, and between Condition and Schedule, F(4,15) = 3.67, were also significant. Neither the other main effect, nor the other interactions, proved to be statistically significant (all ps > .10). As both interactions including the Condition (baseline versus auditory stimulus) factor were significant, further two-way ANOVA (Schedule × Condition) were conducted for each stage, with the appropriate corrections for the degrees of freedom (Howell, 1992, p.449). The main effect of Condition was significant in all stages. In both Stage 1 (F(1,15) = 14.82), and Stage 3 (F(1,15) = 6.48), the baseline condition produced a higher rate than the Tone condition; whereas in Stage 2 (F(1,15) = 9.43) the click condition produced a higher rate than the baseline condition. The main effect of Schedule was significant in Stage 1, F(4,15) = 5.38, and Stage 2, F(4,15) = 4.59, but not in Stage 3, F(4,15) = 2.53. The interaction of these two factors was not significant in any of the Stages, ps > .05. Table 1 displays the results of the least square linear regression analyses. Although based on a small number of points and, hence, only tentative, three consistent tendencies were found in these regressions. First, all regressions fitted well to each set of data (all VACs > 95%). All slope values were lower than 0.8 indicating that under-matching occurred. The intercepts generally were larger than zero, indicating a response bias to the left lever. Finally, the slope values revealed the reinforcer sensitivity
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Table 1 Log response ratios (y) as a function of log obtained reinforcer ratios (x), in each stage, and each condition of Experiment 1 Response allocation Stage 1 Baseline Stage 1 Tone Stage 2 Baseline Stage 2 Click Stage 3 Baseline Stage 3 Tone 2
y = 0.061 + 0.638x (VAC = 95.6%) y = 0.051 + 0.741x (VAC = 99.3%) y = 0.051 + 0.598x (VAC = 99.5%) y = 0.037 + 0.519x (VAC = 95.8%) y = 0.062 + 0.587x (VAC = 99.5%) y = 0.063 + 0.670x (VAC = 98.3%)
All data shown were the average over the last 5 sessions in each group. Equations for the regression analyses are given with the variances accounted for in parentheses.
during Tone was higher than that during its baseline, whereas the slope value during Click was lower than that during its baseline. In summary these data show that the tone and click stimuli had different effects on responding: a loud tone suppressed, and a click facilitated, responding. These data suggest that the type of an auditory stimulus may be important in determining its effect on responding, in addition to its intensity (see also McAdie et al., 1993). They also support previous demonstrations of the effects of tones and clicks on rats’ behavior (Reed et al., 1995); the former stimulus suppressed behavior, whereas the latter stimulus facilitated responding. Thus, to the extent that the tone served to suppress responding and enhance sensitivity to reinforcement (as indexed by the shift in the matching behavior of the rats) it appears to function in a similar manner to an electric shock. 4. Experiment 2 It should be noted that the extent of the suppressive effect of a tone in Experiment 1 was not large. Certainly, it might be expected that responding would be suppressed to a greater degree by the superimposition of a foot shock. If a tone could be employed in this context to facilitate research into aversive control of behavior, it would be helpful if a stronger effect could be noted. Reed et al. (1995, 1996) found a large suppressive effect when the tone was presented during extinction. In the present Experiment 1, however, the tone was introduced on relatively rich reinforcement schedules. As noted in the General introduction, the suppressive effect of a response-contingent tone may be stronger on leaner schedules (see also Reed and Yoshino, 2001). Experiment 2 was designed to investigate whether the suppressive effect of a loud tone varies as a function of the reinforcement schedule. That is, does a larger suppressive effect occur under a lean reinforcement schedule after extended training. 5. Method 5.1. Subjects and apparatus Sixteen experimentally naive, male Lister Hooded rats served. The subjects were 7–8 months old at the start of training, had a free-feeding body weight range of 445–595 g. Other details regarding subjects and apparatus were as described in Experiment 1.
5.2. Procedure The first two stages of two magazine training sessions were identical to those in Experiment 1. Following this, subjects were divided into four experimental groups (n = 4) counterbalanced for response rates to the two levers, and for the response allocations on the basis of the last three sessions of the conc. VI 15-s VI 15-s schedule. Subjects then received further pre-training. Throughout these stages each group consistently received a relative reinforcement allocation of 3:1, 2:1, 1:2, or 1:3 on the two levers. The schedules for each group in each stage are summarized in Table 2. Each session lasted 40-min, and a 2-s COD was in effect. The experimental treatment included four stages, each consisting of eight Baseline sessions, eight Tone sessions, and five Recovery sessions. The reinforcement schedules for each group in each stage also are summarized in Table 2. During the Tone sessions, each group received a conc. VI 60-s VI 60-s schedule of tone presentation along with each reinforcement schedule. The intensity of the tone was 105 dB[A] and its length was 1.5s throughout the stages. Each session lasted 40-min, and a 2-s COD applied to both the reinforcement schedule and tone presentation schedule. The Tone sessions were followed by five Recovery sessions, during which each group received the same reinforcement schedule as in the Baseline sessions prior to the Tone sessions. 5.3. Data collection and analysis Three variables were recorded during the Baseline and Recovery sessions, and four during the Tone sessions, as described in Experiment 1. The data from the last five sessions in the Baseline or Tone sessions, and the last three sessions in the Recovery sessions, were used to calculate group means for these measures. The data from the Baseline and Recovery sessions were combined to obtain a single mean for each stage, and this was compared with that during the Tone sessions. Other aspects of data collection and analyses were as described in Experiment 1. Table 2 Values of variable interval schedules for each alternative employed during pretraining and experimental stages for each group of Experiment 2 Group 3:1
Group 2:1
Group 1:2
Group 1:3
Left
Right
Left
Right
Left
Right
Left
Right
25 50 75 100 125
75 150 225 300 375
25 50 75 100 125
50 100 150 200 250
50 100 150 200 250
25 50 75 100 125
75 150 225 300 375
25 50 75 100 125
Experimental stages 1 (Lean) 150 2 (Rich) 50 3 (Middle) 100 4 (Lean) 150
450 150 300 450
150 50 100 150
300 100 200 300
300 100 200 300
150 50 100 150
450 150 300 450
150 50 100 150
Pretraining 1 2 3 4 5
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6. Results and discussion Figs. 3 and 4 depict the group-mean response rates for each condition, in each stage, for each reinforcement schedule. The main effect of Stage is shown much more clearly in the averaged response rates across the schedules (Fig. 4). In the six of the eight conditions, the 1:3 reinforcement rate group showed the highest rate of responding, and in seven out of eight conditions the 3:1 group showed the lowest. The rates of responding for the other two groups was not consistent across the conditions. Group-mean response rates increased from Stage 1 (lean schedule) to Stage 2 and 3 (rich and middle schedule), and decreased in Stage 4 when the leaner reinforcement schedule was reinstated. The response rates during the Tone phases were lower than those during the Baseline phases. Regardless the reinforcement schedule employed, every group showed lower levels of responding during the tone phases than that during the baseline phases.
Fig. 3. Overall response rates over the last 5 sessions of each stage, each condition, for each group. 3:1, 2:1, 1:2 and 1:3 refer to ratios of reinforcement schedules for left to right lever, which each experimental groups received. LEAN, RICH, and MIDDLE refer to the reinforcement frequency. BASE = Baseline sessions, TONE = Tone sessions. See Table 2 for schedules in detail.
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As the purpose was to examine the suppressive effect of tone as a function of different reinforcement schedules, twoway ANOVAs for the main effects of Schedule and Condition were conducted, with appropriate modifications for the degrees of freedom (Howell, 1992, p.449). These analyses revealed that the main effect of Condition was significant only in Stage 1, F(1,12) = 10.01, and in Stage 4, F(1,12) = 4.32; that is, during the two lean schedule phases. There was no significant effect of condition in either Stages 2 or 3, ps > .10. These analyses showed no significant main effect of Schedule, ps > .50, and no significant interaction, for any Stage, ps > .20. Results of the least square linear regression analyses are summarized in Table 3. Although needing to be treated with some caution, all regression lines fitted to each set of data well (VAC > 94%). The slope values were generally lower than 1.0, suggesting that under-matching occurred. All intercepts were positive and revealed a response bias to the left alternative. Comparisons of the slope values across conditions revealed slope values generally increased on transfer from Baseline to Tone conditions. In the current experiment the tone suppressed responding, and the degree of suppression varied as a function of the reinforcement schedule. There was greater suppression under leaner reinforcement schedules, but little suppression when reinforcement was more frequent. This effect confirms what was apparent from cross-experimental comparison (cf. Andronico and Forgays, 1962; Reed et al., 1995; Reed and Yoshino, 2001). This effect corroborates that noted in Experiment 1, where tones were found to suppress responding, and suggests that in addition to suppressing responding, a tone also alters sensitivity to reinforcement in a similar manner to an electric shock. This second conclusion should be tempered in that the effect of the tone varied, to some extent, with the order of its presentation. The suppressive effect was greatest during Stage 1 (the leanest schedule), and diminished over the next two stages. However, the suppressive effect did emerge again in the response rate data of Stage 4. This would undermine the suggestion that the effect of tone merely reflected an order effect (possibly due to habituation of the effectiveness of the tone across phases). There are two issues that are worthy of some brief mention. It should be noted that the rates of reinforcement for the LEAN Stages in Group 3:1, and in Group 1:3, was actually one third Table 3 Log response ratios (y) as a function of log obtained reinforcer ratios (x), in each stage, and each condition of Experiment 2 Response allocation Stage 1 Baseline Stage 1 Tone Stage 2 Baseline Stage 2 Tone Stage 3 Baseline Stage 3 Tone Stage 4 Baseline Stage 4 Tone
Fig. 4. Overall response rates over the last 5 sessions averaged across groups of each stage and each condition. Error bars display the standard errors of mean. LEAN, RICH, and MIDDLE refer to the reinforcement frequency. See Table 2 for schedules in detail.
y = 0.065 + 0.797x (VAC = 98.9%) y = 0.079 + 0.911x (VAC = 97.4%) y = 0.046 + 0.808x (VAC = 99.6%) y = 0.092 + 0.862x (VAC = 99.7%) y = 0.059 + 0.879x (VAC = 100%) y = 0.062 + 0.924x (VAC = 97.7%) y = 0.048 + 0.805x (VAC = 99.2%) y = 0.028 + 0.857x (VAC = 99.3%)
All data shown were the average over the last 5 sessions in each group. Equations for the regression analyses are given with the variances of accounted for in parentheses.
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greater overall, compared to those rates in that stage for Group 2:1, and Group 1:2 (i.e. 600 vs. 450). Therefore, if the current findings regarding the impact of the density of reinforcement on the effectiveness of the tone as a punisher held, it might be expected that Groups 3:1 and 1:3 would show a less suppression than the two 2:1 groups. Inspection of Fig. 3 shows that, in general, this does seem to hold, although this clearly requires further and more detailed study than is allowed by the numbers of subjects employed in this experiment. Secondly, it may be worth noting that response rates overall were lower in Experiment 2 than in Experiment 1. The reason for this may either be that the rats used in Experiment 2 were older and heavier than those in Experiment 1, or that the schedules employed in Experiment 2 were, in general, leaner than those in Experiment 1. Whatever the reason for this lower rate, it may be the smaller amount of tone-induced suppression found in Experiment 2 was related to this lower response rate (perhaps through the influence of a floor effect). 7. Experiment 3 The third experiment investigated whether the duration of a loud tone affects its suppressive effect. Reed et al. (1995, 1996) used a 1.5-s tone, and showed a suppressive effect of a tone on responding. In contrast, Andronico and Forgays (1962) employed a procedure in which a tone lasted as long as the rat held down the lever, and found a facilitative effect of a tone on responding. To explore this issue, three levels of tone duration were employed to compare the suppressive effects of a tone with such durations to each other. 8. Method 8.1. Subjects and apparatus Twelve experimentally naive, male Lister Hooded rats were used. The subjects were 6 months old at the start of training, had a free-feeding body weight range of 420–490 g. All other details of the subject maintenance, and concerning the apparatus used in this study are as described in Experiment 1.
The Tone sessions were followed by the eight Recovery sessions, during which each group received the same reinforcement schedule as during the Baseline stage. Every session throughout all stages lasted 40-min, and a 2-s COD was effective for both of the reinforcement and tone presentation schedules. 9.1. Data collection and analysis Data concerning three variables were recorded during each session of each Phase as described in Experiment 1. The data from the last four sessions in each stage, and from the first four sessions in the Tone and Recovery sessions, were used to calculate group means for these measures. 10. Results and discussion Fig. 5 depicts the overall group-mean response rate during the last four sessions in each stage. Response rates during Baseline and Recovery were at similar levels among the groups. The response rate during Tone was lower in Group 0.5, and Group 1.0, but the response rate during Tone was higher in Group 3.0. A two-way ANOVA (duration × condition) revealed no main effects, ps > 0.40, but a significant interaction, F(2,4) = 8.27. The simple effect of condition for each group were significant: F(2,6) = 7.75, for Group 0.5; F(2,6) = 5.41, for Group 1.0; and, F(2,6) = 6.40, for Group 3.0. To examine the suppressive effect of the tone, Newman–Keuls’ Tests revealed that the differences between Baseline and Tone, and Tone and Recovery, were significant for Groups 0.5 and 3.0. For Group 1.0, the comparison between Tone and Recovery was significant, but that between Baseline and Tone was not. No significant effect was obtained in the comparison between Baseline and Recovery for any group. These results demonstrate that a short-duration tone produced a suppressive effect, and the long-duration tone produced a facilitative effect, on responding (see also Reed and Yoshino,
9. Procedure Each subject received three pre-training stages as described in Experiment 1. The experimental treatments included three stages: twenty sessions of Baseline, eight sessions of Tone, and eight sessions of Recovery. All rats received a conc. VI 180-s VI 180-s schedule throughout the experimental sessions. After 10 Baseline sessions, the subjects were divided into three experimental groups (n = 4). These groups were counterbalanced for response rates and response allocations during the last 5 of these sessions. During the Tone sessions, each rat received a conc. VI 60-s VI 60-s schedule of tone presentation along with the reinforcement schedule. A 0.5-s tone was employed for rats in Group 0.5; 1.0s for those in Group 1.0; and 3.0-s for those in Group 3.0. The intensity of the tone was 105 dB[A] for all groups.
Fig. 5. Overall response rates over the last 4 sessions of each stage, for each group of tone duration. Error bars display the standard errors of mean. 0.5, 1.0, and 3.0 denote the duration of the tone employed during the Tone sessions for each group (in seconds). BASE = Baseline sessions, TONE = Tone sessions, RECOV = Recovery sessions.
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2001). This provides further evidence of the punishing effect of a tone, establishing that a tone will be suppressive if it is short. Concerning the facilitative effect of 3.0-s tone, three explanations could be considered. Firstly, the hedonic value of the tone may have increased with its duration. Secondly, the longer tone may have facilitated the arousal level of rats. Thirdly, the operation of a coincidental escape contingency may explain the facilitative effect of the tone. Some responses during the tone presentation may have been adventitiously reinforced by the termination of the tone (see Baron, 1991). Although this last assumption appears plausible, it is not clear whether this kind of contingency existed in the current experiment, and additional speculation is not warranted on the basis of the present data. 11. General discussion The present series of studies was designed to confirm the conditions under which an auditory stimulus would serve as a punishing stimulus for operant behavior. This investigation was motivated by the need to find a more acceptable aversive cue than an electric shock, in order to facilitate the investigation of aversively controlled behavior. Also, it was motivated by the issues suggested by cross-experimental comparison of studies of the effects of auditory stimuli on instrumental responding. The current studies demonstrated that both the type, and duration, of a loud auditory stimulus were important in determining its suppressive effect on instrumental responding. Experiment 1 noted that a response-dependent tone, but not a click, suppressed ongoing instrumental responding (see also Reed et al., 1995). Experiment 3 noted that short rather than long stimuli produced a suppressive effect on responding (see also Reed and Yoshino, 2001). That longer duration tones facilitate responding is consistent with previous work (Andronico and Forgays, 1962). In addition, as well as the properties of the auditory stimulus, the value of the reinforcement schedule over which it is superimposed, determine its effect on responding. Experiment 2 demonstrated that the suppression was greatest under leaner schedules of reinforcement (Reed and Yoshino, 2001). Thus, a brief loud tone has a suppressive effect under a lean reinforcement schedule. These results help to explain several of the discrepant findings in the sensory reinforcement literature reported in the general introduction. Moreover, these results demonstrate that an auditory stimulus may serve as a functional punisher for behavioral studies of learning. In addition to the general suppressive effect on responding, the present data show, albeit tentatively, that a tone shifts the preference towards a richer alternative (see Experiments 1 and 2). Studies using an electric shock as a punisher also consistently show such a preference shift (De Villiers, 1980; Farley, 1980). Although the results obtained from these studies do indicate that a loud brief tone can be used as a punisher when the experimental settings are well chosen, the magnitude of the effects observed was quite small. This may result from the use of intermittent punishment schedules in all studies, which is
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typically less pronounced than the effect of punishment applied to every response (see Azrin and Holz, 1966, for a thorough discussion). However, if the effect could be enhanced in future work, then it could offer a more ethically acceptable stimulus through which to study punishment. It should be noted that rats hearing is damaged, by noises loader than 110 dB, only after 5 days constant exposure (Cappaert et al., 2000), and so the current short durations of auditory stimulation should not present such a physical risk to the animals. Given this, the use of auditory stimuli may be a solution to the problem noted by Pierce and Epling (1995, p.241), who note that: “On the basis of animal ethics, investigations of punishment have almost been eliminated at the basic level”. In order to conduct investigations of the effect of punishment, it would be appropriate, and valid, if a loud, short-duration tone was used to punish responses maintained by a relatively lean reinforcement schedule. Acknowledgements These data were collected as part of a thesis, submitted in requirement of a doctorate, by the second author, at University College London. Thanks are due to Lisa A. Osborne and Andy Lattal for their support and comments. Correspondence concerning this article should be addressed to: Phil Reed, Department of Psychology, Swansea University, Singleton Park, Swansea, SA2 8PP, U.K. (e-mail: [email protected]). References Andronico, M.P., Forgays, D.G., 1962. Sensory stimulation and secondary reinforcement. The Journal of Psychology 54, 209–219. Azrin, N.H., Holz, W.C., 1966. Punishment. In: Honig, W.K. (Ed.), Operant Behavior: Areas of Research and Application. Appleton-Century-Crofts, New York, pp. 380–447. Baron, A., 1991. Avoidance and punishment. In: Iversen, I.H., Lattal, K.A. (Eds.), Experimental Analysis of Behavior (Part1). Elsevier Science Publishers, Amsterdam, pp. 173–217. Baum, W.M., 1974. On two types of deviation from the matching law: Bias and undermatching. Journal of the Experimental Analysis of Behavior 22, 231–242. Cappaert, N.L.M., Klis, S.F.L., Muijser, H., Kulig, B.M., Smoorenburg, G.F., 2000. Noise induced hearing loss in rats. Noise and Health 3, 23–32. Davison, M., McCarthy, D., 1988. The Matching Law: A Research Review. Lawrence Earlbaum, Hillsdale, NJ. De Villiers, P.A., 1980. Toward a quantitative theory of punishment. Journal of the Experimental Analysis of Behavior 33, 15–25. Farley, J., 1980. Reinforcement and punishment effects in concurrent schedules: a test of two models. Journal of the Experimental Analysis of Behavior 33, 311–326. Howell, D.C., 1992. Statistical Methods for Psychology, 2nd Ed. PWS-Kent Publishing, Boston, MA. McAdie, T.M., Foster, R.M., Temple, W., 1996. Concurrent schedules: qualifying the aversiveness of noise. Journal of the Experimental Analysis of Behavior 65, 37–55. McAdie, T.M., Foster, R.M., Temple, W., Matthews, L.R., 1993. A method for measuring the aversiveness of sounds to domestic hens. Applied Animal Behaviour Science 27, 223–238. Pierce, W.D., Epling, W.F., 1995. Behavior analysis and learning. Prentice Hall, Englewood Cliffs, NJ. Reed, P., Collinson, T., Nokes, T., 1995. Aversive properties of auditory stimuli. Learning and Motivation 26, 101–115.
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Reed, P., Mitchel, C., Nokes, T., 1996. Intrinsic reinforcing properties of putatively neutral stimuli in an instrumental two-levers discrimination task. Animal Learning & Behavior 24, 38–45. Reed, P., Yoshino, T., 2001. The effect of response-dependent tones on the acquisition of concurrent behavior in rats. Learning and Motivation 32, 255–273.
Reed, P., Yoshino, T., 2005. Effects of contingent tone on concurrent schedule performance at different deprivation levels. European Journal of Behaviour Analysis, 6. Symmes, D., Leaton, R.N., 1962. Failure to observe reinforcing properties of sound onset in rats. Psychological Reports 10, 458.