Net Amount of Food Affects Autoshaped Response Rate, Response Latency, and Gape Amplitude in Pigeons

The contribution of net amount of food to conditioned response strength and topography was assessed in four pigeons under autoshaping contingencies. In each session, under one baseline phase and three replication phases, three trial types were presented sequentially: One conditioned stimulus (keylight) signaled one small pellet, another signaled one large pellet, and a third signaled seven small pellets which were weight-matched to one large pellet. Five dependent variables were response rates and latencies based on the occurrence of both keyswitch closures and gapes (beak openings) and gape amplitudes. In result, net amount of food, not pellet diameter or number, affected all dependent variables. Notably, gape amplitudes elicited by the seven-small pellet keylights were larger than the gape amplutides elicited by the one-small pellet keylights even though the gape amplitudes elicited by both unconditioned stimuli (one or seven pellets) were equally small. This mismatch between conditioned and unconditioned responses is incompatible with stimulus substitution accounts but is compatible with an associative strength account. Furthermore, the changes in the dependent variables were most likely determined by Pavlovian and not by inadvertent operant contingencies. The findings demonstrate that an analysis of classical conditioning benefits from the inclusion of topographical measures.     

Summation in Autoshaping with Short- and Long-duration Stimuli

Five autoshaping experiments with pigeons examined the effects of presenting in compound two stimuli that had individually been paired with food. The rate of responding during the compound was the same as for the individual stimuli when the stimulus duration was 10 sec. When the duration of the stimuli was 30 sec, the compound elicited a higher response rate than its components. This enhanced rate of responding during the compound was evident only for the initial portion of each trial. Moreover, the enhanced rate of responding was no greater than for a compound composed of an excitatory and a neutral element. These results present difficulties for both elemental and configural theories of conditioning.     

The role of context in intertrial interval effects in autoshaping

Two experiments evaluated the role of differential conditioning of the context in mediating the effect of intertrial interval (ITI) in autoshaping. In Experiment 1 pigeons were given acquisition with two keylights, each presented in a particular context. A given keylight/context combination had associated with it either a short (10-sec) or a long (2-min) ITI. Acquisition was more rapid with the long ITI. Tests with those keylights in a common third context indicated that the longer ITI had resulted in greater conditioning. On the other hand, pigeons trained on keylights with mixed ITIs in a third context evoked more responding when they were tested in the short ITI context compared with the long ITI context. That suggests that a context with a history of a short ITI enhances performance. In Experiment 2, two keylights were initially conditioned with mixed ITIs and then extinguished in different contexts under different ITI lengths. Extinction was more rapid for the keylight presented with a short ITI. That difference persisted when the keylights were tested with mixed ITIs in a common third context, suggesting a difference in associative strength of the keylights. The results are interpreted in terms of differential context conditioning resulting in differences in learning about the keylight.     

Resurgence of time allocation

The resurgence of time allocation with pigeons was studied in three experiments. In Phase 1 of each experiment, response‐independent food occurred with different probabilities in the presence of two different keylights. Each peck on the key changed its color and the food probability in effect. In Phase 2, the food probabilities associated with each keylight were reversed and, in Phase 3, food was discontinued in the presence of either keylight. The food probabilities were .25 and .75, in Experiment 1, and 0.0 and 1.0 in Experiment 2. More time was allocated to the keylight correlated with more probable food in Phases 1 and 2, and in Phase 3 resurgence of time allocation occurred for two of three pigeons in Experiment 1, and for each of four pigeons in Experiment 2. Because time had to be allocated to either of the two alternatives in Experiments 1 and 2, however, it was difficult to characterize the time allocation patterns in Phase 3 as resurgence when changeover responding approached zero. In Experiment 3 this issue was addressed by providing a third alternative uncorrelated with food such that in each phase, after 30 s in the presence of either keylight correlated with food, the third alternative always was reinstated, requiring a response to access either of the two keylights correlated with food. In this experiment, the food probabilities were similar to those in Experiment 1. Resurgence of time allocation occurred for each of three pigeons under this procedure. The results of these experiments suggest that patterns of time allocation resurge similarly to discrete responses and to spatial and temporal patterns of responding.     

Discrimination and differentiation of response number in stimulus directed pecking of pigeons.

In Experiment 1, autoshaping trials terminated with food only if pigeons emitted more than a target number of responses during a trial in one condition and fewer than a target number in another. The median number of responses per trial shifted in accordance wtih the requirements. The responding of yoked-control birds that received response-independent reinforcers did not vary with the response requirements. In Experiment 2, the number of responses in autoshaping trial became the discriminative stimulus for reinforcement in the second component of a chained schedule. In one condition, responding was reinforced only if the number of responses in the first component was above a target value; in the other condition, responding was reinforced only if the number was below the target value. The distribution of the first-component response numbers did not shift systematically between discrimination conditions, but response rates in the second component indicated that the number of responses in the autoshaping trial was a discriminable property behavior.     

A comparison of pecking generated by serial, delay, and trace autoshaping procedures

Pigeons were exposed to serial, delay, and trace autoshaping procedures. In Experiment I, all conditioned stimuli (CSs) were changes in illumination of the response key. The number of trials to acquisition of the keypeck increased from serial, to 4-sec delay, 8-sec delay, and 8-sec trace procedures, in that order. In Experiment II, which used a longer intertrial interval, trials to criterion increased from 8-sec delay, to 28-sec delay, 8-sec trace, and 28-sec trace procedures, in that order. In Experiment III, two groups received serial procedures in which the first CS was either a tone or a houselight, and the second was a keylight. The tone group acquired the key peck more rapidly than the houselight group. Early in conditioning in these experiments, and when the conditioned stimulus was a change in the keylight, there was a short latency to the onset of pecking and pecking was directed at the CS. After extensive conditioning, or when the CS was relatively diffuse, pecking still occurred, but had a longer latency and was not reliably directed toward the conditioned stimulus.     

Context effects on choice.

Four pigeons responded on a concurrent-chains schedule in four experiments that examined whether the effectiveness of a stimulus as a conditioned reinforcer is best described by a global approach, as measured by the average interreinforcement interval, or by a local contextual approach, as measured by the onset of the stimulus preceding the conditioned reinforcer. The interreinforcement interval was manipulated by the inclusion of an intertrial interval, which increased the overall time to reinforcement but did not change the local contingencies on a given trial A global analysis predicted choice for the richer alternative to decrease with the inclusion of an intertrial interval, whereas a local analysis predicted no change in preference. Experiment 1 examined sensitivity to intertrial intervals when each was signaled by the same houselight that operated throughout the session. In Experiment 2, the intertrial interval always was signaled by the stimulus correlated with the richer terminal link. In Experiment 3, the intertrial interval was signaled by the keylights correlated with the initial links and two novel houselights. Experiment 4 provided free food pseudorandomly during the intertrial interval. In all experiments, subjects' preferences were consistent with a local analysis of choice in concurrent chains. These results are discussed in terms of delay-reduction theory, which traditionally has failed to distinguish global and local contexts.     

Visual dominance in inhibitory conditioning in the pigeon

In a conditioned inhibition paradigm (A+, B+, AX?_, pigeons received either of two keylight stimuli reliably followed by food (A+, B+). However, when one of these keylights was accompanied by another stimulus, food did not follow (AX?). For some groups, the putative inhibitor was a tone, whereas for others it was illumination of a red houselight. The birds pecked the A and B stimuli at a high rate. When X was red houselight, the birds pecked A at a much lower rate in the presence of X. When X was a tone, discrimination between A and AX was much poorer. Moreover, in a transfer test, red houselight inhibited responding to the other keylight, B, but tone did not. These results indicate that red houselight becomes a conditioned inhibitor more quickly than tone in appetitive situations, just as red houselight becomes a conditioned excitor more quickly in those situations. These results contradict the assertion that the latter outcome occurs because red houselight is a stronger appetitive excitor than tone at the start of the experiment (the “head start” hypothesis).     

Acquisition of the autoshaped key peck as a function of amount of preliminary magazine training

Three experiments evaluated the effect of magazine training on acquisition of the pigeon's key peck during autoshaping. In Experiment I, pigeons were exposed to two days of extended magazine training, followed on the third day by keylight-only presentations. All pigeons pecked the keylight early in the keylight-only session. Experiment II examined the relationship between the number of magazine-training trials and trials to the first peck. Pigeons were given either 0, 3, 10, or 25 magazine-training trials followed by the standard autoshaping procedure. The number of trials to the first peck was related to the number of magazine-training trials. In Experiment III, pigeons were exposed to the standard autoshaping procedure without prior magazine training. The data from Experiment III suggested that key pecking will occur only after the response of eating from the lighted hopper has occurred. Taken together, these results suggest that initial magazine training is an important variable in autoshaping. Key pecking is discussed as a generalized consummatory response.     

Sources of visual interference in delayed matching-to-sample with pigeons

In two experiments, independent groups of pigeons were trained on an identity matching task involving line orientations as sample and comparison stimuli. For some birds an overhead houselight was illuminated continuously throughout each training session. For other birds the houselight was never illuminated during training sessions. During subsequent testing, the lighting conditions during the delay were the same as in training on some trials, but on other trials they were opposite those of training during either the entire delay (Experiment 1) or during a portion of the delay (Experiment 2). In birds trained with the houselight off, turning the houselight on during the delay produced a large and enduring disruption in matching accuracy. On the other hand, in birds trained with the houselight on, turning the houselight off during the delay produced only a moderate and temporary disruption in matching accuracy. These findings are inconsistent with the prevailing view that retroactive interference in pigeons is a function of a change in illumination level relative to that which prevailed during training. In pigeons, as in monkeys, sustained retoactive interference effects obtain only when the level of illumination is increase during the delay interval.     

The influence of partial reinforcement on serial autoshaping with pigeons

The effect of partial reinforcement on the rate of responding during the first element of a serial compound was investigated using autoshaping in pigeons. Experiment I employed the illumination of a response key by two different colours as the elements of the compound. Responding during the first element was faster when this stimulus was intermittently paired with the second element and the unconditioned stimulus than when a continuous reinforcement schedule was employed. Experiment II demonstrated that this effect of partial reinforcement is unaffected by maniuplating the associative strength of the second element at the outset of compound conditioning. A similar effect of partial reinforcement was also found in Experiment III which used a tone as the first element of the serial compound.     

Effect of delay-interval stimuli on delayed symbolic matching to sample in the pigeon

In Experiment 1, food-deprived pigeons received delayed symbolic matching to sample training in a darkened Skinner box. Trials began with the illumination of the grain feeder lamp (no food sample), or illumination of this lamp, accompanied by the raising of the feeder tray (food sample). After a delay of a few seconds, the two side response keys were illuminated, one with red and one with green light, with positions counterbalanced over trials. Pecking the red (green) comparison produced grain reinforcement if the trial had started with food (no food); pecking red after a no-food sample or green after a food sample was not reinforced. Once matching performance was stable, four stimuli were presented during the delay interval, and their effects on matching accuracy were evaluated. Both illumination of the houselight and the center key with white geometric forms decreased matching accuracy, whereas presentation of a tone and vibration of the test chamber did not. In Experiment 2, pecking the red center key was reinforced with food according to a variable interval schedule. The effects of occasional brief presentations of the four stimuli used in the first experiment on ongoing pecking were assessed. The houselight and form disturbed key pecking, but the tone and vibration did not. Thus, stimuli that interfered with delayed matching also interfered with simple operant behavior. Implications of these results for theories of remembering are discussed.     

Autoshaping as a function of prior food presentations

Young chickens were given 1, 10, 100, or 1000 presentations of grain in a hopper. Subsequently, the key was illuminated before each presentation of grain to study autoshaping of the key-peck response. The number of keylight-grain pairings before a bird first pecked the lighted key was found to be a U-shaped function of the number of prior food-only presentations, with pecks occurring significantly sooner after 100 food-only trials than after any of the other values. Two of five chicks at the 100-trial value pecked on the first illumination of the key. Experiment II showed further that when a series of food-only trials (no keylight) preceded keylight-only trials (no food) 30% of the chicks pecked the illuminated key. Experiment III extended the generality of first-trial pecking to pigeons. After preliminary training with food-only, two of five pigeons pecked on the first illumination of a key. The results suggest a close relationship between autoshaping and pseudo-conditioning.     

Spatial contiguity facilitates Pavlovian second-order conditioning

Two experiments investigated the effects of spatial contiguity upon the formation of second-order conditioning in pigeon subjects. Experiment 1 used an autoshaping procedure to pair two visual stimuli, S2 and S1, after S1 had previously been paired with food. The resulting second-order conditioning of S2 was superior when both stimuli appeared on the same response key within a trial, compared with their appearing on different keys. Experiment 2 found a similar importance of spatial contiguity between S2 and S1 in a conditioned suppression paradigm. In addition, consistently presenting S2 and S1 in the same spatial location produced superior conditioning compared with varying their spatial relation from trial to trial. The design of these experiments was such as to imply that spatial contiguity facilitates performance by improving the formation of association rather than by promoting stimulus generalization or pseudoconditioning. Moreover, the observation of a facilitative effect of spatial contiguity between S1 and S2 in two different paradigms that use qualitatively different unconditioned stimuli and evoke different responses implies some generality for these findings. Consequently, these results suggest that spatially contiguous stimuli are especially associable in Pavlovian conditioning paradigms.     

The role of preliminary magazine training in acquisition of the autoshaped key peck

A series of experiments tested the hypothesis that initial key pecks in the autoshaping procedure are generalized pecks at the illuminated grain hopper. Experiment I found that autoshaping readily occurred when the chamber was continuously illuminated by a house-light. In Experiment II, pigeons given magazine training and autoshaping with an unlighted grain hopper failed to autoshape in 200 trials. Acquisition of autoshaped key pecking was retarded in Experiment III when stimulus control by the magazine light was reduced. In the fourth study, pigeons were given magazine training with either a red or white magazine light and then given autoshaping with concurrently presented red and white keys. For all pigeons in this experiment, the first key peck occurred on the key of the same color as that pigeon's magazine light. The results of these experiments were interpreted as supporting an account of autoshaping that identifies initial key pecks as arising due to generalization of pecking at the lighted grain hopper to pecking at the lighted key.     

Choice as a dependent measure in autoshaping: sensitivity to frequency and duration of food presentation.

Previous investigations have shown that rate, latency, and percentage of trials with at least one response are somewhat insensitive measures of the strength of autoshaped responding. In the present studies, these measures were contrasted with the allocation of responding during simultaneous choice tests, a measure of response strength frequently used in operant paradigms. In two experiments, nine pigeons were exposed to a forward pairing autoshaping procedure. Training sessions consisted of the successive presentation of three stimuli, each followed by food on either 100%, 50%, or 0% of the trials. Choice testing involved the simultaneous presentation of the three stimuli. In Experiment I, all pigeons consistently directed their initial choice responses and the majority of subsequent responses to the stimulus always followed by food, despite the fact that during training sessions the response rates of most birds were highest in the presence of the stimulus followed by food on 50% of the trials. In Experiment II, rate, latency, and percentage of trials with at least one response did not change appreciably as a function of duration of feeder presentations. However, choice responding was lawfully affected by duration of feeder presentations. These data suggest that choice is perhaps a more sensitive measure of the strength of autoshaped responding than other, more commonly employed, indices.     

Aspects of the reinforcer learned in second-order Pavlovian conditioning

Four experiments used an autoshaping procedure in pigeons to explore learning about the reinforcer in a second-order conditioning paradigm. Experiment 1 conditioned two visual second-order stimuli (S2), using as reinforcers two visual first-order stimuli (S1), each of which had previously been paired with food. Animals for which the S2 stimuli were each consistently paired with one particular S1 developed second-order responding more rapidly than did animals for which the identity of S1 varied from trial to trial. Moreover, following consistent pairings, extinction of an S1 had a depressive effect upon second-order responding which was peculiar to the S2 with which it had been paired. Both results suggest that in this preparation the organism identifies a particular S1 as the reinforcer for each S2. The remaining experiments examined the details of that identification. A compound S1, itself composed of two separable elements, was used to reinforce an S2. Subsequent extinction of either element of S1 led to a depression in the responding to S2, which indicates that both elements were involved in the second-order conditioning. Moreover, the use of several complex discriminations, which produced different behavior to S1 and to its elements, suggested that the organism had associated the S2 with the compound S1 rather than with its separate elements. However, even complete extinction of the response to S1 left some residual behavior to S2, which indicates that a portion of the second-order conditioning is independent of the current state of the reinforcer. These results demonstrate that in some situations the organism associates a conditioned stimulus with a rich representation of the reinforcer.     

Effects of food-pellet size on rate,latency, and topography of autoshaped key pecks and gapes in pigeons.

Four pigeons responded under autoshaping contingencies in which different conditional stimuli (red or green keylights) were associated with unconditional stimuli of different magnitudes (large or small food pellets) over successive trials within a session. Both topography (beak opening or gape) and strength (rates and latencies of key pecks and gapes) of responding during the conditional stimuli depended on the magnitude of the correlated unconditional stimulus. Key-peck and gape rates were higher and latencies were shorter in large-pellet trials than in small-pellet trials. Gape amplitudes varied directly with pellet size, although conditional and unconditional gapes were larger than either pellet. These findings were replicated when the key colors were presented either on one or two keys and after reversals of the color-size correlations. Because the unconditional stimulus was varied through pellet size, magnitude was not confounded with food-access duration or quality. These results demonstrate the effects of the magnitude of the unconditional stimulus, in that rates and latencies of both key pecks (which are directed movements toward the key) and gapes (which are independent of the bird''s position and key properties) varied with pellet size. Gape measures were unique in that two dimensions (response strength and topography) of a single response class varied simultaneously with magnitude.     

Conditioned approach and withdrawal behavior in pigeons: Effects of a novel extraneous stimulus during acquisition and extinction

Three experiments examined the effects of complete removal of reinforcement and of the introduction of a novel stimulus on conditioned approach and withdrawal behavior exhibited by pigeons in an autoshaping paradigm. Experiment 1 indicated that complete omission of food from the experimental situation resulted in the gradual disappearance of both approach and withdrawal behavior in subjects that had received either explicitly paired or explicitly unpaired conditioning. Subsequent presentation of a novel visual stimulus reinstated both approach and withdrawal. Experiment 2 replicated these findings in a within-subjects, discriminative paradigm. In Experiment 3, presenting the novel visual stimulus during acquisition when approach and withdrawal behaviors were asymptotic did not produce significant disruption of performance. These data suggest that removal of reinforcement leads to the disappearance of withdrawal as well as approach performance, and that subsequent presentation of a novel stimulys reinstates whatever behavior was dominant prior to extinction—a finding that seems analogous to results of experiments concerning proactive interference.     

Duration discrimination is better with food access as the signal than with light as the signal

In Experiment 1 a go/no-go discrimination procedure was used to compare control of five pigeons' keypecking by food-access duration with control by light duration. Pecks to an illuminated key were reinforced with grain following 10-sec presentations of food access or houselight, but not after 5-sec presentations of either stimulus. Each subject discriminated food-access duration faster and to a greater degree than light duration. In four between-subject replications, pigeons discriminated food-access duration better than the duration of a localized light, the feeder light and a keylight, and with either water or food as reinforcement. In Experiment 2 control by durations of food access and light was compared using a conditional right-left choice procedure (two pigeons), and a delayed symbolic matching-to-sample procedure (six pigeons). Under both, choice accuracy again was higher on food-access trials. The results of Experiment 3, in which two pigeons received generalization trials with durations of food access and light that were intermediate to the training values, confirmed that responding was controlled by the duration dimension of both food access and light. The superior control by food access is consistent with previous evidence that food is an effective and memorable stimulus, possibly because of its biological importance. These results also provided empirical support for the commonly made assumption that stimuli differ in effectiveness. As well, the results show that the stimulus to be discriminated can play an important role in the accuracy of duration disciminations, a fact which has implications for the study of temporal discriminations in animals.