Minimization of modal contours: an essential cross-species strategy in disambiguating relative depth

Two chromatically identical patterns, a diamond and a ladder, were shown on a computer touchscreen. Domestic hens were reinforced for pecking at the pattern that was the highest up on a grid that provided pictorial depth information, i.e. on the pattern that to a human appears as being the furthest away. Every tenth trial was a non-rewarded probe trial with the two patterns partially overlapping. In the absence of other cues depth stratification can occur on the basis of a minimization of interpolated occluding contours. In humans the diamond is usually perceived to be in front of the ladder because shorter interpolated contours are needed to account for the occlusive effect of the diamond on the ladder. The hens pecked more often at the ladder during the probe trials. The results suggest that the avian and mammalian visual systems operate along similar principles when dealing with the problem of solving occlusion indeterminacy in chromatically homogeneous patterns. Received: 26 March 1999 / Accepted after revision: 17 September 1999     

Learning of an oddity rule by pigeons in a four-choice touch-screen procedure

Six pigeons were trained to peck at a target (odd stimulus) that was presented on a touch-screen together with three identical distractors (non-odd stimuli). The target could be either a square or a circle that was either blue or green, and the distractors in each trial were always of the opposite form and color to the target. Thus, the birds could solve the task by attending to color, form, or both. Transfer tests showed that performance was not disrupted by novel forms, stimulus sizes, distractor numbers, and display configurations, but broke down with novel stimulus types (textured stimuli, clip art images, and photographs). Transfer to novel colors was, for the most part, restricted to trials in which only one component—target or distractors, but not both—had a novel color. This suggested that the pigeons used a couple of if–then rules rather than an oddity concept to solve the task, and that color differences between target and distractors were the only cue upon which responding was based. A control experiment with the order of color and form tests being reversed excluded the possibility of the prevalence of color being an artifact of task order and reinforcement contingencies.     

The control of food-caching behavior by Western scrub-jays (Aphelocoma californica)

Western scrub-jays (Aphelocoma californica) did not show extinction when caching behavior was never rewarded and they had no choice of where to cache the food. However, when the jays had the choice of caching items in 2 different locations or during 2 successive episodes, and only 1 of each was always rewarded at recovery, they rapidly learned to cache in the rewarded location or episode. When the jays had learned during training trials that their caches were always moved to 1 of 2 locations they did not cache in, then on the test trial they cached in the location that had been previously rewarded. To test whether these jays avoided the location in which their caches had been pilfered or chose the rewarded location, the procedure was repeated to include a 3rd location that was never rewarded. The jays avoided the pilfered location but cached equally in the rewarded and nonrewarded locations.     

Oddity learning by African dwarf goats ( Capra hircus)

Seventeen African dwarf goats (adult females) were trained on oddity tasks using an automated learning device. One odd stimulus and three identical nonodd stimuli were presented on a screen divided into four sectors; the sector for the odd stimulus was varied pseudorandomly. Responses to the odd stimulus were deemed to be correct and were reinforced with food. In phase 1, the goats were trained on eight stimulus configurations. From trial to trial the odd discriminandum was either a + symbol or the letter S, and the nonodd discriminandum was the symbol not used as the odd one. In phase 2, the animals were similarly trained using an unfilled triangle or a filled (i.e., solid black) circle. In phase 3, three new discriminanda were used, an unfilled, small circle with radiating lines, an unfilled heart-shaped symbol, and an unfilled oval; which of the three discriminanda was odd and nonodd was varied from trial to trial. Following these training phases, a transfer test was given, which involved 24 new discriminanda sets. These were presented twice for a total of 48 transfer test trials. Results early in training showed approximately 25% correct, which might be expected by chance in a four-choice task. After 500-2,000 trials, results improved to approximately 40-44% correct. The best-performing subject reached 60-80% correct during training. On the transfer test, this subject had 47.9% correct and that significantly exceeded 25% expected by chance. This finding suggests that some exceptional individuals of African dwarf goats are capable of learning the oddity concept.     

Required pecking alters judgments of the passage of time by pigeons

There is evidence that how humans perceive time is affected by the activity in which they are engaged when they are judging time. In humans, typically, the more demanding the task, the faster time seems to pass. We asked whether a similar effect could be found in pigeons. Pigeons were trained to discriminate between a short-(2-sec) and a long-(10-sec) duration stimulus. Depending on the color of the stimulus (white or blue), the pigeons were required to peck (at least once per second or the trial was aborted) or to refrain from pecking (pecks aborted the trial). Once these tasks had been acquired to a high degree, probe trials involving white and blue stimuli were presented at durations between 2 and 10 sec. On trials in which the pigeons were required to peck, the point of subjective equality (i.e., the point at which pigeons are equally likely to choose the stimulus associated with long stimuli as the stimulus associated with short stimuli) was almost 1 sec longer than on trials in which the pigeons were required to refrain from pecking. In other words, on trials that required pecking, more time passed before the pigeons indicated that the probe duration was at the subjective midpoint between 2 and 10 sec than on trials that did not require pecking. This result suggests that like humans, the pigeons underestimated the passage of time when they were active or when attention to time-related cues had to be shared with attention to satisfying the response rate requirement.     

Pigeons flexibly time or count on cue

In Experiment 1, pigeons were presented with a sequence of light flashes and cued to peck a key for reward either after a fixed time or after a fixed number of flashes. Curves that showed the rate of key pecking over time within trials indicated that peak rates of response were reached near the fixed time on timing-cued trials and near the fixed number of flashes on counting-cued trials. In Experiment 2, the key cue was shifted from timing to counting or from counting to timing midway through a trial. The peak times reached after the cue change indicated that pigeons kept track of time while cued to count but did not count while cued to time. These findings suggest a basic asymmetry in the dual-mode model of timing and counting.     

Redundant information in an observing-response procedure

In three observing-response experiments relevant to the information hypothesis of conditioned reinforcement, the basic procedure was one in which an observing response produced one stimulus on trials that terminated in non-contingent reinforcement and another stimulus on trials that terminated in a brief timeout. In Experiment I, the observing response consisted of a single peck or a short fixed-ratio schedule (FR 3 or FR 6), depending on the type of trial. If the single peck produced the negative stimulus and the fixed ratio produced the positive stimulus, observing responses were maintained. If the single peck produced the positive stimulus and the fixed-ratio produced the negative stimulus, observing responses were not maintained on negative trials. In the second experiment, the response key was either white or dark at the beginning of a trial, indicating whether it was a positive or negative trial. Observing responses continued to be maintained on positive trials but not on negative trials. In Experiment III, only positive or negative trials were scheduled for several sessions. Observing responses extinguished regardless of whether positive or negative trials were scheduled. The results do not support the hypothesis that making the stimuli produced by observing responses redundant will reduce observing responses.     

Does attention follow the motion in the “shooting line” illusion?

When a line is presented in the vicinity of a recent luminance change (peripheral cue), it is perceived to be drawn over time away from its “cued” end even though the line is actually presented all at once. This study was designed to determine whether attention, exogenously attracted to the cue, would come under the exogenous control of this illusory motion and follow the drawing motion from the cued end to its terminus. Each trial began with the display of four small squares at the corners of an imaginary square centered about fixation. On the critical trials, one of the four squares brightened briefly, after which a horizontal line was presented joining either the two upper or the two lower squares. Shortly thereafter, the distribution of attention was determined by asking the observer to indicate the nature of a change that was equally likely to occur to one of the squares. Responses to targets presented at a noncued location that was at the end of an illusorily drawn line were as fast as those to targets at the cued location and were much faster than those to targets at the remaining noncued locations. This pattern was not shown when the line preceded the cue, strongly suggesting that attention follows the motion in this illusion.     

Does attention follow the motion in the "shooting line" illusion?

When a line is presented in the vicinity of a recent luminance change (peripheral cue), it is perceived to be drawn over time away from its "cued" end even though the line is actually presented all at once. This study was designed to determine whether attention, exogenously attracted to the cue, would come under the exogenous control of this illusory motion and follow the drawing motion from the cued end to its terminus. Each trial began with the display of four small squares at the corners of an imaginary square centered about fixation. On the critical trials, one of the four squares brightened briefly, after which a horizontal line was presented joining either the two upper or the two lower squares. Shortly thereafter, the distribution of attention was determined by asking the observer to indicate the nature of a change that was equally likely to occur to one of the squares. Responses to targets presented at a noncued location that was at the end of an illusorily drawn line were as fast as those to targets at the cued location and were much faster than those to targets at the remaining noncued locations. This pattern was not shown when the line preceded the cue, strongly suggesting that attention follows the motion in this illusion.     

Ordinal Position Learning and Remote Anticipation

Rats were runway trained on each of two 3-trial series of reward outcomes. The series are labeled XNY and ZNN, for which X represents a trial that was rewarded with Noyes pellets and N represents a trial that ended with no reward. Units of distinctively flavored breakfast cereals served as reward on trials labeled Y and Z. One group (Floor) had each series occur with a correlated runway floor, either smooth and black or rough and white. For a second group (Memory), the floor cue was uncorrelated with series. Animals in both groups learned to approach the goal rapidly on the 1st trials of the 2 series and slowly on the 2nd trials, but only Group Floor learned to differentiate the 3rd trials of the series. These results recommend a view of serial learning that emphasizes the role played by information about the ordinal position of series items.     

Ordinal position learning and remote anticipation

Rats were runway trained on each of two 3-trial series of reward outcomes. The series are labeled XNY and ZNN, for which X represents a trial that was rewarded with Noyes pellets and N represents a trial that ended with no reward. Units of distinctively flavored breakfast cereals served as reward on trials labeled Y and Z. One group (Floor) had each series occur with a correlated runway floor, either smooth and black or rough and white. For a second group (Memory), the floor cue was uncorrelated with series. Animals in both groups learned to approach the goal rapidly on the 1st trials of the 2 series and slowly on the 2nd trials, but only Group Floor learned to differentiate the 3rd trials of the series. These results recommend a view of serial learning that emphasizes the role played by information about the ordinal position of series items.     

Balancing cognitive control: How observed movements influence motor performance in a task with balance constraints

We investigated the influence of observed movements on executed movements in a task requiring lifting one foot from the floor while maintaining whole-body balance. Sixteen young participants (20–30 years) performed foot lift movements, which were either cued symbolically by a letter (L/R, indicating to lift the left/right foot) or by a short movie showing a foot lift movement. In the symbol cue condition, stimuli from the movie cue condition were used as distractors, and vice versa. Anticipatory postural adjustments (APAs) and actual foot lifts were recorded using force plates and optical motion capture. Foot lift responses were generally faster in response to the movie compared to the symbol cue condition. Moreover, incongruent movement distractors interfered with performance in the symbol cue condition, as shown by longer response times and increased number of APAs. Latencies of the first (potentially wrong) APA in a trial were shorter for movie compared to symbol cues but were not affected by cue-distractor congruency. Amplitude of the first APA was smaller when it was followed by additional APAs compared to trials with a single APA. Our results show that automatic imitation tendencies are integrated with postural control in a task with balance constraints. Analysis of the number, timing and amplitude of APAs indicates that conflicts between intended and observed movements are not resolved at a purely cognitive level but directly influence overt motor performance, emphasizing the intimate link between perception, cognition and action.     

An infrared system for the detection of a pigeon''s pecks at alphanumeric characters on a TV screen: the dependency of letter detection on the predictability of one letter by another.

Three pigeons pecked at letters of the alphabet and at the symbol "?" displayed on a computer-driven cathode ray screen. A 4 by 4 matrix of infrared emitting and detecting diodes and associated circuitry identified the location of a pigeon''s responses to the screen. Responses at the target letter T were probabilistically reinforced with food whenever T appeared in a string of three letters in the middle of the screen. Responses at the symbol "?" appearing below this string were probabilistically reinforced whenever T did not appear. The letter F anywhere in the three-character string either strongly predicted the occurrence of the target letter T, in two conditions, or predicted its nonoccurrence, in a third. This manipulation of the frequency with which the familiar letter F predicted T was shown to change the function relating probability of a correct peck at the symbol "?" to the number of Fs in the string. This effect may be interpreted as an instance of the phenomenon where an organism''s acquired knowledge changes what it sees.     

No evidence for a cue mismatch in negative priming

An experiment is reported in which the cue mismatch hypothesis of negative priming, an important novel variant of the mismatching hypothesis, was tested. A cue mismatch and a no mismatch condition were contrasted in a visual discrimination task. In the prime display of cue mismatch ignored-repetition trials, the colour of the prime distractor was different from the colour of the cue indicating the selection feature (coloured square). In probe displays, cue and repeated stimulus had the same colour. In the no mismatch condition, the visual cue was neutral in terms of colour (always black), so that there was always no cue mismatch between prime and probe displays. Contrary to the prediction of the cue mismatch hypothesis, the negative priming effect was not larger in the cue mismatch than in the no mismatch condition. The cue mismatch hypothesis must therefore be rejected. In contrast, the episodic retrieval account is consistent with the results.     

试次历史对跨通道非空间返回抑制的影响

个体对刺激的反应不仅受刺激本身的影响, 还会受到先前刺激的影响, 表现为对当前试次中刺激的反应会受到前一试次的影响, 即试次历史。本研究采用“线索-中性线索-靶子”范式探讨前一试次有效性对跨通道的非空间返回抑制的影响。实验1通过连续两个试次间的线索有效性考察在跨通道非空间返回抑制中试次历史的影响。为了在跨通道非空间返回抑制中减小试次历史的影响, 实验2通过延长试次间时间间隔考察跨通道非空间返回抑制中试次历史的作用是否减小。结果发现, 前一试次线索无效时, 当前试次中的返回抑制效应量显著小于前一试次有效时, 这种影响会根据试次中线索和靶子通道的不同而不同。并且当延长试次间的时间间隔可以有效地减少前一试次对当前试次的影响。因此本研究表明, 试次历史能够对跨通道非空间返回抑制产生影响, 并且这种影响可以通过增大试次间时间间隔来减小。     

Spontaneous alternation and pattern of reinforcement

In Experiment I, rats were given one pair of trials per day in a T-maze; group RN were rewarded on the first trial only, NR were rewarded on the second trial only, while RR were rewarded on both trials. Alternation was approximately the same for all groups, and there was little decline in alternation over 28 days. There was, however, a difference in the choice behaviour on trials when rats failed to alternate, NR and RR, but not RN, choosing according to a position preference. These results are incompatible with several earlier theories of spontaneous alternation, and the hypothesis was put forward that alternation is initially part of an exploratory tendency, but that, when the maze becomes explored, the exploratory tendency dies down, and alternation only continues when rats have been reinforced (primarily or secondarily) for alternating. This hypothesis was tested in a second experiment, similar to the first but in which one group of rats was not rewarded on either trial; as predicted, this group showed significantly more decline in alternation than rewarded rats.     

A theoretical analysis of the PAN ambiguous-cue problem

The PAN ambiguous-cue problem consists of three stimuli: P, the positive (consistently rewarded) cue; N, the negative (consistently nonrewarded) cue; and A, the ambiguous cue which is negative (nonrewarded) when paired with P, but positive (rewarded) when paired with N. This paper demonstrates how the finding of superior performance on the NA trials as compared to the PA trials (with stereometric objects) can be rigorously derived from a recent extension of Hull-Spence discrimination learning theory, the Stimulus Interaction Hypothesis. It is also shown how this theory can account for the converse outcome of better performance on PA than on NA trials when planometric plaques are used as stimuli. Finally, alternative explanations of the findings are described and evaluated.     

Integrating rewards and cognition in the frontal cortex

Research indicates that the dorsolateral prefrontal cortex (DLPFC) contributes to working memory and executive control, whereas the ventral frontal cortex (VFC) contributes to affective and motivational processing. Few studies have examined both the functional specificity and the integration of these regions. We did so using fMRI and a verbal working memory task in which visual cues indicated whether recall performance on an upcoming trial would be linked to a monetary reward. On the basis of prior findings obtained in delayed response tasks performed by nonhuman primates, we hypothesized that (1) VFC would show an increase only in response to a cue indicating potential for a monetary reward; (2) DLPFC would show sustained activity across a delay interval for all trials, though activity in rewarded trials would be enhanced; and (3) regions engaged in speech-based rehearsal would be relatively insensitive to monetary incentive. Our hypotheses about DLPFC and rehearsal-related regions were confirmed. In VFC regions, we failed to observe statistically significant effects of reward when the cue or delay epochs of the task were examined in isolation. However, an unexpected and significant deactivation was observed in VFC during the delay epoch; furthermore, a post hoc voxelwise analysis indicated a complex interaction between (1) the cue and delay epochs of the task and (2) the reward value of the trials. The pattern of activation and deactivation across trial types suggests that VFC is sensitive to reward cues, and that portions of DLPFC and VFC may work in opposition during the delay epoch of a working memory task in order to facilitate task performance.     

Inhibition of return to color: A replication and nonextension of Law, Pratt, and Abrams (1995)

We presented subjects with an unpredictive cue that was followed after a 150- to 900-msec interstimulus interval (ISI) by a detection target. Cue and target were blue or red squares that appeared at fixation and in an otherwise uniform black field. In a filler condition, a task-irrelevant filler stimulus (magenta square) was presented during the ISI; in a no-filler condition, no stimulus appeared during the ISI. Using only a 900-msec ISI, Law, Pratt, and Abrams (1995) reported slower reaction times (RTs) when cue and target were the same color, but only when the task-irrelevant filler was presented during the ISI. They argued that attention is first drawn to the cue color and that inhibition of return (IOR; see Posner & Cohen, 1984) is established when attention is drawn away from that cue color representation by the task-irrelevant filler. Critical to their view is the assumption that IOR occurs only after attention is drawn away from the cue color by the filler. Assuming a time course for the withdrawal of attention from the cue color representation, Law et al. ’s view predicts growth of the inhibitory effect as a function of ISI in the filler condition as well as facilitation at early ISIs in the no-filler condition (because there is no filler to withdraw attention from the cue color). Contrary to these predictions, we found that the inhibitory effect observed by Law et al. at the 900-msec ISI was present at—and did not vary in magnitude across—the range of ISIs tested. And there was never facilitation in the no-filler condition. These results challenge Law et al. ’s inference that IOR for foveally presented colors was operating in their paradigm.