Journal of Comparative and Physiological Psycholoy 1975, Vol. 89, No. 10, 1180-1191

Form Preferences in Successive Discrimination Learning of Young Chicks James F. Zolman, David G. Pursley, Joyce A. Hall, and Christie L. Sahley Department of Physiology and Biophysics, Medical Center, University of Kentucky In four experiments the effects of form and orientation pecking preferences of 1- and 3-day old Van tress X Arbor Acre chicks on successive discrimination learning were determined, using heat reinforcement. Major findings were as follows: (a) The young chick has both circle and vertical orientation pecking preferences that are present during at least the first 3 days after hatching; (b) when either of these preferred cues is the nonreinforced cue, the young chick has difficulty in learning not to respond to it but learns quickly not to respond to an unpreferred cue (e.g., triangle and horizontal oriented dots or bar); and (c) these pecking preferences can be modified by heat reinforcement, and the effects of this conditioning is evident in subsequent extinction and retention tests. The main conclusion from these experiments is that form and orientation preferences, like brightness and color preferences, are important developmental constraints on conditioning of the young chick.

Therefore, in the typical pecking preference test without any external reinforcement, a large number of socially tested birds are used to obtain reliable results. But even when food reinforcement is used with grouptested chicks, the replicability of the results still remains questionable. For example, Hess (1964) has reported that pecking preferences of the young chick can be changed quickly by reinforcing, with food, pecks to the nonpreferred cue. When this modification is given to chicks that are 3-5 days old, over 80% of all pecks during subsequent extinction are to the previously reinforced normally nonpreferred cue (Hess, 1964). Attempts to replicate this permanent modification of the chick's pecking preference, however, have not been successful. In these studies, chicks given reinforcement training between the ages of 3-5 days either This work was supported by Grant MH-24260 revert to the normally preferred cue during from the National Institute of Mental Health and extinction, stop responding consistently to by the Human Development Studies Program of either cue, or show rapid extinction to the the College of Medicine, University of Kentucky, previously reinforced cue (Frank & Meyer, with funds granted by the Foundations' Fund for 1970; Meyer & Frank, 1970; Brown & Research in Psychiatry (T64-205). The authors are grateful to D. Black, S. Curtis, K. Martyno- Brown, Note 1). Also while Gottlieb (1971) wicz, and P. Murphy for their assistance during has questioned seriously the experimental use behavioral testing, and to D. McFarland for his of chicks because of unknown and unconassistance in data reduction and analysis. trolled variables that affect the replicability llequest for reprints should be sent to James of results, he has stressed recently the F. Zolman, Department of Physiology and Biophysics, Medical Center, University of Kentucky, importance of the ontogeny of species-typical perceptual preferences, particularly their Lexington, Kentucky 40506. 1180

Color and form preferences in the pecking behavior of young birds have been reported in a number of studies (see Fantz, 1965; Hess, 1973; Hinde, 1970, for reviews). Most of the preference data on color (Hess, 1956, 1964; Hess & Gogel, 1954; Oppenheim, 1968) and on form (Fantz, 1957; Goodwin & Hess, 1969) are based on a large number of group-tested birds. The necessity of using a large number of birds has been justified because of the tremendous variability in specific preferences of different hatches of the same breed of chicks. Likewise, a grouptesting procedure has been justified because of the low response rates of individually tested chicks. Supposedly, only when large numbers of chicks are tested socially in batches of 30-75 chicks and many pecks are obtained is consistency of pecking preferences achieved (Goodwin & Hess, 1969).

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FORM PREFERENCES IN YOUNG CHICKS prenatal origin (Gottlieb, 1973). Unfortunately, very few studies have been concerned with a prenatal ontogenetic analysis of avian preferences, perhaps because of the difficulty of reliably measuring postnatal preference responding in individual chicks. Recently, however, it has been shown that form approach preferences and brightness approach preferences of young chicks can be determined by using heat reinforcement procedures (Zolman, 1969; Zolman & Lattin, 1972). In these approach-preference studies, chicks were individually tested and consistent findings were obtained with as few as 10 chicks in each preference group. Thermal reinforcement procedures have also been developed to condition key pecking of young chicks in successive discrimination problems using discrete conditioning trials (Zolman, Chandler, & Black, 1972). The purpose of this study, therefore, was to determine whether there are any interactive effects among form preferences and successive discrimination learning of the young chick using heat reinforcement procedures. Four experiments are reported in which the age of the chick, the stimuli used, or the reinforced and nonreinforced cues were varied. In two experiments, retention or extinction tests were given to determine whether the young chick retained the effects of any conditioned modification of its initial pecking preference. Since these studies were completed over a 3-yr period, the long term replicability of this preference data was also established. EXPEEIMENT 1

With group-tested chicks, round stimuli elicit preferentially pecking responses, and this preference has been reported to remain constant during at least the first posthatch week (Fantz, 1957; Goodwin & Hess, 1969). Therefore, the objectives of this experiment were to determine whether the 1-day-old chick tested individually on a successive circle-triangle discrimination has a circle preference, whether this preference can be modified by heat reinforcement, and whether the modification of any initial preferential responding is retained.

A-KEY B-PROJECTOR C-HOUSE LIGHT D-REINFORCEMENT LIGHT

7

FIGUBE 1. Schematic representation of discrimination box for key-peck conditioning of young chicks, using heat reinforcement.

General Method Subjects and rearing procedure. Vantress X Arbor Acre chicks were incubated and hatched at 37-38 °C and 56%~60% relative humidity. Each chick was removed from the dark hatching incubator and banded within 4 hr after hatching. Chicks from different hatches extending over a 3-yr period were used in these form-discrimination experiments. All chicks were reared socially in groups of 10-12 in white Plexiglas brooder compartments (56 X 33 X 23 cm) in a Tyler temperature-controlled room set at 35 °C (Experiments 1 and 4) or in communal cages of a standard 35 °C brooder (Experiments 2 and 3). Food and water were available ad lib, and the brooder room and communal brooder were illuminated from 6 a.m. to 11 p.m. Apparatus. Behavioral testing was performed in four discrimination boxes designed for testing young chicks, using heat reinforcement (Figure 1). The boxes used in Experiments 2 and 3 have been described previously (Zolman et al., 1972). In the other experiments to be reported, each of the discrimination boxes was housed individually in a Forma Scientific incubator (Model 3665) in which the ambient temperature was set at 10 °C (±1 "C). 1 Another Forma Scientific incubator 1

Experiments 1, 2, 3, and 4 were run during January 1972, July 1970, March 1971, and Novem-

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HEAT SOURCE

2. Schematic representation of heat-delivery system to the four discrimination incubators. with an auxiliary 2,000-W heater was set at 38 °C, and plastic tubing (20 and 10 cm) connected each cold incubator with this heat source (Figure 2). A push-pull fan arrangement (two fans, each 500 cfm) in the heat incubator was used to maintain a balanced flow of warm air to each discrimination incubator. The temperature of the air under each discrimination box was maintained at 35 °C and was monitored continuously by a Yellow Springs air thermometer (Model 502) connected to a Yellow Springs telethermometer. The ambient temperature on the wire floor of each discrimination box was maintained at 10 °C and was also monitored continuously. Heat onset in each discrimination box was controlled by two separate Ledex rotary solenoids that when activated, displaced two 10-cm-diam. circular butterfly valves. One valve instantaneously diverted the warm 35 °C air up through the discrimination box, whereas the other valve opened to replace in the air-flow system the same amount of warm air diverted. Consequently, air flow in this system was balanced so that reinforcement delivered in any of the discrimination boxes did not affect the flow of warm air to the other boxes. A 2-W light bulb located under each discrimination box was also turned on so that reinforcement consisted of both heat and light onset. A small Rotron whisper fan (65 cfm) located 25 cm above the open top of the disber 1973, respectively. Experiment 1 replicated the preference data of an experiment run during March 1970. This replication indicated that changes in the housing of the discrimination boxes and in the delivery of heat had no significant effects on the young chick's preferential responding.

crimination box was turned on immediately after reinforcement and remained on during the intertrial interval. This fan dispersed any residual heat remaining in the discrimination box after reinforcement. A white masking noise of 78 dB re 20 /jN/m2 was delivered through a 10-cm speaker on the back wall of each discrimination incubator. Response keys were adjusted to be activated with less than 8 g of force and were mounted directly on IEE 12-unit inline projectors which were used to present the stimuli on the transparent keys. Stimulus-reinforcement contingencies were programmed and controlled by BRS electronics solid-state modules, and response latencies of the chicks in .1 sec were recorded on four printout counters. Procedure. Behavioral testing included autoshaping the young chicks to peck the response key and then testing on a successive discrimination. On each day the chicks were removed from their home brooder 1 hr before training and isolated in individual, white Plexiglas cylinders (20 X 15 cm). These cylinders were placed under fluorescent lights, and a masking white noise was delivered through speakers. The purpose of this procedure was to acclimate the chicks to social isolation and to white noise before discrimination training. After each training session, the chicks were returned to their isolation cylinders to minimize experience with interfering stimuli. The autoshaping procedure used was similar to that described by Brown and Jenkins (1968) and consisted of equal number of presentations, in a semirandom sequence, of each of the two test stimuli. The autoshaping sequence of events was

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(a) key light onset; (b) 16-seo intrastimulus dura- the S—, and for the other chicks the white triangle tion; (c) key light offset with 8-sec reinforcement was the S-f and the white circle was the S—. (35 °C air and light); (d) 5-sec intertrial interval Statistical analysis. All analyses were performed (ITI) with house light on; (e) key light onset, etc. on mean response latencies of six trial blocks of When the chick pecked the key at any time during each stimulus condition (S + , S — ) , and an analythe 16 sec intrastimulus duration, reinforcement sis of variance with repeated measures was used was delivered immediately and a new trial was to determine significance levels. Since each chick begun after the 5-sec ITI. During autoshaping and received 312 S+ and 312 S— presentations over throughout the experiment, the chick was given the 3-day testing period, this block analysis was a "free" reinforcement while being placed in the performed on the mean response latencies of 52 test box. Two autoshaping sessions, the first to a S+ and 52 S— data points for each chick. Retencriterion of six responses or 24 trials and the sec- tion and extinction results, when available, were ond session for 24 trials, preceded discrimination analyzed separately. In the first experiment an training. Chicks that gave at least six responses analysis of variance of the first day's performance during the second autoshaping session were used was also done. In this case, the block analysis was in subsequent discrimination testing (Zolman done on the mean response latencies of 12 S+ and 12 S— data points for each chick. et al., 1972). Three discrimination sessions of 48 trials were Experiment 1. In the first experiment 24 Vangiven on the first day of training and five sessions tress X Arbor Acre chicks, 1 day old (25.1 hr; of 48 trials were given on both the second and SD = .9), were tested on the circle-triangle sucthird day of training. The stimuli were presented cessive discrimination. Three days after the last during each training session in a Fellows' (1967) discrimination session, the chicks were given a sequence. Generally, this sequence may be de- single 48-trial retention test with the cue-reinscribed as having runs of S+ or S— trials not forcement contingency the same as during acquiexceeding three in length and as having equal sition training. In this experiment for one half probability of an S+ or S— trial given that the of the chicks the white circle was the S+ and the previous trial was either an S+ or S — ; that is, white triangle was the S — , with the cue-reinforcethe two stimuli in any successive discrimination ment contingency reversed for the rest of the were presented equally in a semirandom order chicks. that controlled for single and/or double alternation responding. The sequence of events on a trial Results and Discussion during discrimination training was the same as during autoshaping with two modifications: (a) Mean response latencies of six trial blocks No "free" reinforcements were presented at the termination of the 16-sec intrastimulus duration for the circle S + chicks and the triangle S + and (b) responses on trials in which the S— was chicks are presented in Figure 3. As can be presented were not reinforced, rather the chick seen, both groups learned this successive was held in the dark chamber for 8 sec. When the discrimination; however, chicks in the circle chick failed to respond on any trial, the 5-sec ITI S+ group learned more quickly than those was initiated and 16 sec was recorded for that trial. On training days the intersession interval in the triangle S+ group. An analysis of was between 30 and 45 min, during which time the variance test across the 13 discrimination chicks were returned to their isolation cylinders. sessions indicated a high degree of S + , S — At the conclusion of the last isolation period of differential performance, F(l, 22) = 21.14, the day, the chicks were returned to their home p < .001, with this latency difference brooders. Preference groups. Three different pairs of increasing as a function of training, Reinstimuli were used in these experiments and in- forcement X Session interaction, F(12, cluded: (a) a white, 10-mm-diam. circle on a red 264) = 15.47, p < .001. While there was no background and a white, equilateral triangle significant difference in S+ and S— re(10-mm sides) on the same red background, (b) three small white dots (4.8-mm diam., spaced 1.6 sponding between the two preference groups mm apart) in a vertical orientation on a red across all 13 discrimination sessions, Group background and the same triplet of dots in a X Reinforcement interaction, F(l, 22) = horizontal orientation on the same red back- 3.64; Group X Reinforcement X Session ground, and (c) a white bar (3.2 X 22 mm) presented vertically on a red background and the interaction, F(12, 264) = .60; there was a same bar presented horizontally on the same red significant difference between these groups background. early in acquisition (first three discrimination Chicks that reached the autoshaping criterion sessions) with the chicks in the circle S + were randomly assigned to the two preference group showing a greater separation in S + conditions within each discrimination experimental design, e.g., for one half of the chicks the and S— responding than chicks in the white circle was the S+ and the white triangle was triangle S+ group, Group X Reinforcement

1184

ZOLMAN, PURSLEY, HALL, AND SAHLEY

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FIGURE 3. Mean response latencies of six trial blocks for chicks that were tested on a circle-triangle successive discrimination when 1-3 days old. (For one half of these chicks the circle was the S+, while for the other chicks the triangle was the S+.)

interaction, F(l, 22) = 7.80, p < .01. Since the only difference between these two groups during training was the reversal of the reinforced and nonreinforced cues, it is evident that the young chick prefers to peck at the circle rather than the triangle during the early phase of training. This initial circle preference, however, can be modified by heat reinforcement, and with extended training the young chick can learn to peck more quickly at the reinforced triangle than at the nonreinforced circle. In the retention test the young chicks retained the effects of the prior discrimination training, which indicates that the modification of the circle preference lasted for at least 3 days; that is, differential responding to S+ and S— was retained, F(l, 22) = 22.78, p < .001, and there was no significant difference between the two preference groups in this differential responding to S+ and S—, Group X Reinforcement interaction, F(l, 22) = 1.98. Therefore, young chicks trained to peck a nonpreferred cue to receive heat do not revert to their original circle preference after a short rest interval. These results, therefore, confirm the circle preference reported in 1-3 day-old chicks tested in large social groups without any external reinforcement (Fantz, 1957; Goodwin & Hess, 1969). More importantly, this "roundness" preference can be obtained in a small number of chicks tested indi-

vidually in a discrete-trials situation. Indeed, this circle preference of the young chick has been obtained in three separate experiments within a 3-yr period.2 It is evident, therefore, that the successive discrimination procedure used is not significantly affected by minor changes in hatches of the same breed of chicks or in seasonal fluctuations of preferences; that is, although unknown nonspecific effects may change slightly the response patterns of chicks tested at different times, the circle preference of the young chick still emerges in spite of these changes. EXPERIMENT 2 In addition to this roundness preference, there is suggestive evidence that preferential responding of young birds occurs also to the orientation of a stimulus; for example, herring and laughing gull chicks peck more at vertical- than horizontal-oriented beaks or rods (Schmerler & Hailman, 1965; Tinbergen & Perdeck, 1950), whereas Arctic tern chicks peck slightly more at horizontal- than vertical - oriented rods (Quine & Cullen, 1964). The purpose of this experiment, therefore, was to determine 2

Chicks tested when 3-5 days old on the successive circle-triangle discrimination also have a significant circle preference during the initial phase of testing, which with subsequent training can be modified by heat reinforcement. The results of this experiment are available from the authors upon request.

FORM PREFERENCES IN YOUNG CHICKS

whether the 1-day-old chick has an orientation preference when cues are presented successively and, if so, whether the preference can be modified by reinforcement. Method Subjects and rearing procedures. Twenty-two Vantress X Arbor Acre chicks were incubated, hatched, and reared socially in communal cages of a standard 35 °C brooder under the conditions described in General Method. All chicks began testing when 1 day old (23.4 hr; SD = .8). Apparatus, procedure, and groups. The apparatus used in this experiment was similar to that in Experiment 1 except that heat was delivered by a small heat box under each discrimination box and the discrimination boxes were housed in the Tyler temperature-controlled room set at 10 °C (±2 °C). A description of this heat-reinforcement delivery system has been described previously (Zolman et al., 1972). The autoshaping and training procedure was the same as described in Experiment 1 with the following exceptions: (a) The vertical and horizontal dots cues were used in the discrimination and (b) no retention test was given. For 11 chicks the vertical cue was the S+ and the horizontal cue the S — , whereas for the other chicks the reinforced and nonreinforced cues were reversed.

Results and Discussion Mean response latencies of six trial blocks for the 1-day-old chicks trained with vertical S + and those trained with horizontal S + are presented in Figure 4. At the end of training, the chicks were showing differential 16.0

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responding to their respective S + and S — cues, reinforcement effect, F(l, 20) = 57.28, p < .001, but there was a greater difference in this S+ and S— responding for the vertical S+ than for the horizontal S+ chicks, as indicated by a significant Group X Reinforcement interaction, F(l, 20) = 38.75, p < .001. For example, the average difference between S+ and S— responses across all 13 discrimination sessions for the vertical S+ chicks was 7.3 sec., whereas this difference for the horizontal S+ chicks was only .7 sec. Sessions, Reinforcement X Sessions, and Group X Sessions were also significant, F(12, 240) = 2.99, p < .001; F(12, 240) = 12.58, p < .001; and F(12, 240) = 3.22, p < .01, respectively. These findings can be understood by considering the significant Group X Reinforcement X Sessions interaction, F(12, 240) = 4.93, p < .001. For the vertical dots S+ chicks, the separation between S+ and S— response latencies was apparent on the first session and increased considerably from one session to the next; but for the horizontal S+ chicks, this latency separation between the S+ and S — did not start to occur until the last few sessions (Figure 4). On the last discrimination session the chicks' latencies to the S + cues were about the same for both the vertical and horizontal S+ groups (2.6 and

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FIGURE 4. Mean response latencies of six trial blocks for chicks that were tested on a vertical-horizontal dots successive discrimination when 1-3 days old. (For one half of these chicks the vertical cue was the S+, while for the other chicks the horizontal cue was the S+.)

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ZOLMAN, PURSLEY, HALL, AND SAHLEY

3.6 sec, respectively); however, the latency preference without any confounding with to the S— was much longer in the vertical the roundness preference. Therefore, 1-dayS+ than the horizontal S+ group (13.3 old chicks were tested on a vertical-horiand 6.1 sec, respectively). Essentially, this zontal bar successive discrimination. finding indicates that 1-day-old chicks have difficulty in not responding to the vertical Method Subjects and rearing procedures. Thirty-two orientation of dots when it is the nonreinforced cue. Based only on the horizontal S+ Vantress X Arbor Acre chicks were incubated, and reared socially under the same congroup's performance, it might have been hatched, ditions as in Experiment 2. All chicks began erroneously concluded that the young chick testing when 1 day old (26 hr; SD = 1.1). has difficulty in discriminating between the Apparatus, procedure, and groups. The apparavertical and horizontal cues and that tus and procedure were the same as in Experinumerous training trials would be necessary ment 2. In autoshaping and training, the only difference between this experiment and Experibefore S+ and S— differential responding ment 2 was that vertical and horizontal white bars could be achieved. That this is not the case on red backgrounds were the discriminative is evident from the very rapid S+ and S — stimuli. For one half of the chicks the vertical bar separation when the horizontal cue is the was the S+ and the horizontal bar the S —, and the other 16 chicks the reinforced and nonreinnonreinforced cue. Also, this orientation for forced cues were reversed. preference appears to be a stronger preference than the circle preference found in the Results and Discussion previous experiments, since this orientation Mean response latencies of six trial blocks preference was significant across all 13 for the 1-day-old chicks trained with the discrimination sessions whereas the circle vertical bar as the S+ and those trained preference was significant across only the with the horizontal bar as the S+ are first three discrimination sessions. presented in Figure 5. Essentially, the same significant results were obtained in this EXPERIMENT 3 experiment as were reported in Experiment In the prior experiment, the young chick 2. These chicks also showed differential S + , showed a significant stimulus preference for S— responding with a greater separation three small dots arranged in a vertical between S+ and S— occurring as training straight line. The purpose of this experiment progressed, reinforcement effect, F(l, 30) was to replicate this vertical orientation = 96.31, p < .001; Reinforcement X

7

BLOCKS OF 6 TRIALS

FIGURE 5. Mean response latencies of six trial blocks for chicks that were tested on a vertical-horizontal bar successive discrimination when 1-3 days old. (For one half of these chicks the vertical cue was the S+, while for the other chicks the horizontal cue was the S+.)

FORM PREFERENCES IN YOUNG CHICKS

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Session interaction, F(12, 360) = 5.57, p < hr; SD = 2.7) under the same conditions as in .001. Overall, the vertical bar S+ chicks Experiment 1. procedure, and groups. The apparahad a greater S+, S — latency separation tusApparatus, and procedure were the same as in Experiment than did the horizontal bar S+ chicks, 1. In autoshaping and training, the only difference Group X Reinforcement interaction, F(i, between this experiment and Experiment 1 was 30) = 10.13, p < .005, and also showed a that the vertical and horizontal white dots on red quicker separation in this differential backgrounds were the discriminative stimuli. Also, immediately after the final discrimination session, responding to S+ and S— as training all chicks were given three extinction sessions of progressed than did the horizontal bar S+ 48 trials. For one half of the chicks the vertical chicks, Group X Reinforcement X Session cue was the S+ and the horizontal cue the S—, interaction, f (12, 360) = 1.98, p < .001. and for the other 11 chicks the reinforced and nonApparently, however, the vertical bar is not reinforced cues were reversed. so strong a preferred cue as the vertical dots; Results and Discussion for example, in the preceding experiment Mean response latencies of six trial blocks there was less than a 1-sec difference in S-ffor the 3-day-old chicks trained with the and S— latencies for the horizontal dots S+ vertical orientation as the S+ and those chicks summed across all sessions, whereas trained with the horizontal orientation as in this experiment there was about a 7-sec the S+ are presented in Figure 6. For these difference in S+ and S— latencies for the older chicks, there was significant differhorizontal bar S+ chicks. ential responding to the S+ and S— cues Based on the results of these last two with quicker response latencies to the S+ experiments, it is evident that the 1-day-old chick has a striking preference for stimuli cue, reinforcement effect, F(l, 20) = presented in a vertical orientation. Thus, 13.97, p < .01, and this differential respondthree small dots or a single bar presented in a ing increased across discrimination sessions, vertical orientation will elicit responses even Reinforcement X Session interaction, F(\2, when these responses are not reinforced. 240) = 7.06, p < .001. While there was no Chicks presented with the same stimuli in a significant Group X Reinforcement interhorizontal orientation, however, quickly action for these older chicks, F(l, 20) = 3.21, learn not to respond when reinforcement is the vertical S+ chicks showed an earlier and larger separation in S+ and S— responding not presented. as training progressed than did the horizontal S+ chicks, Group X Reinforcement X EXPERIMENT 4 Session interaction, F(12, 240) = 2.05, p < The latter two experiments indicated quite .05. Consequently, the vertical preference clearly that the 1-day-old chick has a observed in 1-day-old chicks is also found in striking pecking preference for vertically older 3-day-old socially reared chicks. Thus, oriented stimuli. The purpose of this experi- this vertical orientation pecking preference ment was to determine whether this vertical of young chicks has been obtained in three orientation preference, like the circle prefer- separate experiments completed within a ence, is present during the first three post- 3-yr period, indicating the reliability of this hatch days. Therefore, 3-day-old socially specific visual preference. reared chicks were tested on the verticalThe extinction data also indicate the horizontal dots discrimination. Since this reliability of the prior terminal acquisition experiment was run more than 2 yr after the performance of the two groups (see Figure initial vertical-horizontal dots experiment 7). There was a slight increase in response with the 1-day-old chicks, the long-term latencies across the three extinction sessions, replicability of these stimulus preferences session effect, F(2, 40) = 5.60, p < .01, was also determined. and the significant differential response latencies to the prior S+ and S— cues were Method Subject and rearing procedures. Twenty-two maintained throughout the extinction sesVan tress X Arbor Acre chicks were incubated, sions, reinforcement effect, F(l, 20) = 14.33, hatched, and reared socially until 3 days old (77.2 p < .001. There was no significant group

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effect, F(l, 20) = 1.19, and the Group X trained to pedal step to turn on a flashing Reinforcement, F(l, 20) = 3.07, and Group light, chicks reinforced with a preferred X Reinforcement X Session, F(2, 40) = orange light learned this instrumental 1.03, interactions were also not significant. response in significantly fewer trials than Therefore, from these extinction results it chicks reinforced with a nonpreferred green may be concluded that chicks trained to light. Therefore, it may be concluded that peck at a nonpreferred cue do not begin the young chick has color, form, and orientapecking the normally preferred cue or stop tion preferences that can have profound responding consistently to either cue during effects on the learning of subsequent disextinction. criminations and these preferences may be Based on the results of the preceding regarded as important developmental conexperiments, it is evident that form prefer- straints on conditioning of the young chick. ences can be measured reliably by using heat GENERAL DISCUSSION reinforcement procedures and that there are significant interactive effects among form The young precocial chick has both circle preferences and successive discrimination and vertical orientation pecking preferences learning of the young chick; that is, when that are present at least during the first 3 the preferred cue is reinforced, young chicks days after hatching. Also, these pecking learn quickly to stop responding to the preferences are not affected by minor changes unpreferred S— cue. However, when pecks between hatches of the same breed of chick to the preferred cue are not reinforced (the or by seasonal fluctuations (see Bateson, S —) the young chick has difficulty learning 1974). This question of long-term replicabilnot to respond. ity of preferences in the domestic chick is Similar interactive effects between color important for at least two reasons. First, preferences and discrimination learning have Gottlieb (1971) has stressed the fact that been reported; for example, learning is more unknown and uncontrolled variables affect rapid when approaches of young chicks to the replicability of many results with the preferred color are rewarded than when domestic chicks. Second, Hess (1962, 1964) approaches to the nonpreferred color are has repeatedly emphasized that preferential rewarded (Kovach & Hickox, 1971). like- responding of young chicks may change wise, Bateson and Reese (1969) have between hatches of the same breed of chicks reported that when 1-day-old chicks were and during different seasons of the year

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(Goodwin & Hess, 1969). Thus, in the typical preference test and perhaps even when food reinforcement is used (Frank & Meyer, 1970; Hess, 1964; Meyer & Frank, 1970; Brown & Brown, Note 1), the replicability of results, using the domestic chick, has been a serious problem. Within the successive discrimination procedure, however, preferential pecking responding can be determined with a small number of chicks tested individually, using a discrete-trial situation. Therefore, just like brightness approach preferences (Zolman & Lattin, 1972) and form approach preferences (Zolman, 1969), pecking preferences can be determined reliably, using heat as reinforcement. Now with these heat reinforcement procedures, the effects of prenatal manipulations on species-typical perceptual preferences of the domestic chick could be determined (see Gottlieb, 1973). A consideration of the development of brightness and form approach preferences and the form and orientation pecking preferences reported in this study indicates that no age-dependent generalization can be made regarding preference development in the young chick; for example, brightness approach preferential responding increases as a function of light rearing and consequently 3-day-old, light-reared chicks have a stronger brightness preference than do 1-dayold chicks (Zolman & Lattin, 1972). Conversely, for form approach preferences the 1-day-old chick appears to have a stronger circle preference than the 3-day-old chick (Zolman, 1969). Finally, in this study, the circle and vertical orientation pecking preferences are present during the first 3 days after hatching. Thus, preferential responding of the young Vantress chick may increase or decrease or not change as a function of age. While both of the pecking preferences of the young chick could be modified by heat reinforcement, the circle preference was modified more quickly than was the vertical orientation preference; and thus the circle preference appears to be a weaker preference. Although a number of studies have found preferential responding to stimuli in young chicks, only a few attempts have been made

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BLOCKS OF 6 TRIALS FIGURE 7. Mean response latencies of six trial blocks during extinction for chicks that were tested on a vertical-horizontal dots successive discrimination when 3-5 days old. (For one half of the chicks the vertical cue was the previous S+, while for the other chicks the horizontal cue was the previous S+.)

to modify the young chicks' preferential responding to these stimuli; for example, the brightness preference of young chicks can be modified easily with massed, but not spaced, trials (Zolman & Lattin, 1972). Form and color preferences in the approach behavior of young chicks can be modified with both massed and spaced training trials (Kilham, Klopfer, &0elke, 1968; Taylor, Sluckin, & Hewitt, 1969; Zolman, 1969). Form and color pecking preferences of the chick can also be changed by massed conditioning trials (Frank & Meyer, 1970; Hess, 1964; Meyer & Frank, 1970; Brown & Brown, Note 1). And, as found in this study, orientation pecking preferences can be modified, using a massed-trials procedure. In general, therefore, it has been found that brightness, form, color, and orientation preferences of the young chick can be rather easily changed by conditioning. But it is still not clear whether these modifications are

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transitory or relatively permanent. Unfortunately, it has been assumed that once response modification of preferences has occurred, these learning changes are as permanent as those found following conditioning in the mature organism (see Zolman & Lattin, 1972). However, from the present study it is evident that once the 1-day-old chick has been conditioned to peck the unpreferred triangle in a circle-triangle successive discrimination, this reinforced differential responding is maintained for at least 3 days. Another question related to the permanency of preferences is, what are the visual sensory mechanisms encoding preferential responding in the young chick? Although sensory coding in the adult chicken has not been studied, specific classes of visual detector cells that respond selectively to the orientation of edges or to the direction of movement or to the curvature of the object have been found in the ganglion cells of the pigeon retina (Maturana & Frenk, 1963). Curvature detectors, of course, may play a significant role in the circle preference found for young chicks. The vertical orientation preference found for the young chick would be an excellent species-specific perceptual preference for electrophysiological investigations, since white bars in different orientations and rates of movements are standard stimuli in these neurosensory experiments (Hubel & Wiesel, 1962). Based upon the finding from this study, the vertical orientation of a white bar is a strong preference that remains stable for at least the first three posthatch days, that can be slowly modified by reinforcement procedures, and that can be reliably reproduced behaviorally. This latter characteristic is extremely important when an attempt is made to correlate visual detectors with functional significance as determined by behavioral methods. But it should be emphasized that the discovery and localization of specific classes of visual detector neurons in developing avian sensory systems will not explain preferential responding in the young chick. Implicit in the analysis of perceptual preferences in the young organism is the assumption that sensory mechanisms

are available to encode different stimuli but that the various physical stimuli activating the receptors of the young organism are not quantitatively equivalent with regard to their controlling effect on a particular behavioral pattern (Baerends & Kruijt, 1973). Therefore, while numerous neurophysiological speculations can be made (see Hailman, 1970, for a review), it is quite clear that these conjectures must be tested both electrophysiologically and behaviorally in order to understand the neural mechanisms correlated with preferential responding in the young chick. Indeed, the lack of correlative electrophysiological and behavioral preference studies in birds has permitted much "neurologizing" in the past. Perhaps the reason that these correlative studies have not been done is because of the behavioral unreliability of preferential responding in young chicks tested individually. From the vertical orientation preference results of this study, this reason is no longer valid. REFERENCE NOTE 1. Brown, R. T., & Brown, D. F. Failure to modify pecking preference in chicks. Paper presented at the meeting of the Southeastern Psychological Association, Louisville, April 1970. REFERENCES Baerends, G. P., & Kruijt, J. P. Stimulus selection. In R. A. Hinde & 3. Stevenson-Hinde (Eds.), Constraints on learning. New York: Academic Press, 1973. Bateson, P. P. G. Atmospheric pressure during incubation and posthatch behavior in chicks. Nature, 1974, 248, 805-807. Bateson, P. P. G., & Reese, E. P. The reinforcing properties of conspicuous stimuli in the imprinting situation. Animal Behaviour, 1969, 17, 692-699. Brown, P. L., & Jenkins, H. M. Autoshaping of the pigeon's key peck. Journal of the Experimental Analysis of Behavior, 1968, 11, 1-8. Fantz, R. L. Form preferences in newly hatched chicks. Journal of Comparative and Physiological Psychology, 1957, 50, 422-430. Fantz, R. L. Ontogeny of perception. In A. M. Scrier, H. F. Harlow, & F. Stollnitz (Eds.), Behavior of nonhuman primates (Vol. 2). New York: Academic Press, 1965. Fellows, B. J. Chance stimulus sequences for discrimination tasks. Psychological Bulletin, 1967, 67, 87-92. Frank, L. H., & Meyer, M. E. Food imprinting

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in domestic chicks as a function of social contact Kovach, J. K., & Hickox, J. Color preferences and number of companions. Psychonomic Sciand early perceptual discrimination learning ence, 1970, 19, 293-294. in domestic chicks. Developmental Psychobiology, Goodwin, E. B., & Hess, E. H. Innate visual form 1971, 4, 255-267. preferences in the pecking behavior of young Maturana, H. R., & Frenk, S. Directional movechicks. Behaviour, 1969, 34, 223-237. ment and horizontal edge detectors in the Gottlieb, G. Development of species identification pigeon retina. Science, 1963,1$, 977-979. in birds: An inquiry into the prenatal determina- Meyer, M. E., & Frank, L. H. Food imprinting tions of perception. Chicago: University of in the domestic chick: A reconsideration. PsyChicago Press, 1971. chonomic Science, 1970, 19, 43-45. Gottlieb, G. Introduction to behavioral embryol- Oppenheim, R. W. Color preferences in the peckogy. In G. Gottlieb (Ed.), Behavioral embryoling response of newly hatched ducks (Anas ogy. New York: Academic Press, 1973. platyrhynochos). Journal of Comparative and Hailman, J. P. Comments on the coding of releasPhysiological Psychology, 1968, 66 (3, Pt. 2). ing stimuli. In L. R. Aronson, E. Tobach, IX S. Quine, D. A., & Cullen, J. M. The pecking reLehrman, & J. S. Rosenblatt (Eds.), Developsponse of young Arctic terns Sterna macrura ment and evolution of behavior. San Francisco: and the adaptiveness of the "releasing mechaFreeman, 1970. nism." Ibis, 1964, 106, 145-173. Hess, E. H. Natural preferences of chicks and Schmerler, S., & Hailman, J. P. Discrimination ducklings for objects of different colors. Psyof orientation in the laughing gull, Larus atricilla L. American Zoology, 1965, 5, 655. (Abchological Reports, 1956, 0, 477^83. stract) Hess, E. H. Imprinting and the critical period concept. In E. L. Bliss (Ed.), Roots of behavior. Taylor, A., Sluckin, W., & Hewitt, R. Changing colour preferences of chicks. Animal Behaviour, New York: Hoeber, 1962. 1969, 17, 3-8. Hess, E. H. Imprinting in birds. Science, 1964, Tinbergen, N., & Perdeck, A. C. On the stimulus 148, 1128-1139. situation releasing the begging response in the Hess, E. H. Imprinting: Early experience and the newly hatched herring gull chick (Larus ardevelopmental psychobiology of attachment. New gentatus Pont.). Behaviour, 1950, S, 1-39. York: Van Nostrand-Reinhold, 1973. Hess, E. H., & Gogel, W. C. Natural preferences Zolman, J. F. Stimulus preferences and form discrimination learning in young chicks. Psyof the chick for objects of different colors. Jourchological Record, 1969, 19, 407-416. nal of Psychology, 1954, 88, 483-493. Zolman, J. F., Chandler, S. D., & Black, D. Visual Hinde, R. A. Animal behaviour: A synthesis of discrimination learning of the young chick: ethology and comparative psychology (2nd ed.). Key-peck conditioning with heat reinforcement. New York: McGraw-Hill, 1970. Developmental Psychobiology, 1972, B, 181-187. Hubel, P. H., & Wiesel, T. N. Receptive fields, binocular interaction and functional architec- Zolman, J. F., & Lattin, W. J. Development of brightness preferences in young chicks: Effects ture in the cat's visual cortex. Journal of Physon brightness discrimination learning. Journal iology, 1962, 160, 106-154. of Comparative and Physiological Psychology, Kilham, P., Klopfer, P. H., & Oelke, H. Species 1972, 79, 271-283. identification and colour preferences in chicks. Animal Behaviour, 1968, 16, 238-244. (Received January 13, 1975)