Ramesh S. Bhatt

Conceptual Behavior in Pigeons: Categorization of Both Familiar and Novel Examples From Four Classes of Natural and Artificial Stimuli

Two new procedures—a four-key choice procedure and a four-ply multiple fixed ratio schedule procedure—were used to train pigeons to categorize color slides depicting natural (cat, person, flower) and human-made (car, chair) objects. In Experiments IA, IB, 2A, and 2fl, 16 pigeons trained with 10 slides from each of four categories reliably classified novel examples from these categories. However, performance was more accurate on training than on novel stimuli. In Experiment 3, 8 pigeons learned to classify 2,000 nonrepeating slides. Thus, repetitive training with a limited number of stimuli is not necessary for pigeons to learn a four-category classification task. In Experiment 4, 4 pigeons were trained with a set of repeating slides while concurrently being trained with novel stimuli. As in Experiments IA, IB, 2A, and 2e, performance here was more discriminative on repeatedly seen stimuli than on novel ones. Thus, repetition facilitates categorization, whether or not the pigeons are concurrently exposed to novel stimuli. The implications of these results for models of categorization are discussed. We conclude that the conceptual abilities of pigeons are more advanced than hitherto suspected.

Episodic-like memory in pigeons

It has been proposed that memory for personal experiences (episodic memory, rather than semantic memory) relies on the conscious review of past experience and thus is unique to humans. In an attempt to demonstrate episodic-like memory in animals, we first trained pigeons to respond to the (nonverbal) question “Did you just peck or did you just refrain from pecking?” by training them on a symbolic matching task with differential responding required to the two line-orientation samples and reinforcing the choice of a red comparison if they had pecked and the choice of a green comparison if they had not pecked. Then, in Experiment 1, after providing the conditions for (but not requiring) the pigeons to peck at one new stimulus (a yellow hue) but not at another (a blue hue), we tested them with the new hue stimuli and the red and green comparisons. In Experiment 2, we tested the pigeons with novel stimuli (a circle, which they spontaneously pecked, and a dark response key, which they did not peck) and the red and green comparisons. In both experiments, pigeons chose the comparison appropriate to the response made to the test stimulus. Thus, the pigeons demonstrated that they could remember specific details about their past experiences, a result consistent with the notion that they have the capacity for forming episodic-like memories.

Development of Form Similarity as a Gestalt Grouping Principle in Infancy

Given evidence demonstrating that infants 3 months of age and younger can utilize the Gestalt principle of lightness similarity to group visually presented elements into organized percepts, four experiments using the familiarization/novelty-preference procedure were conducted to determine whether infants can also organize visual pattern information in accord with the Gestalt principle of form similarity. In Experiments 1 and 2, 6- to 7-month-olds, but not 3- to 4-month-olds, presented with generalization and discrimination tasks involving arrays of X and O elements responded as if they organized the elements into columns or rows based on form similarity. Experiments 3 and 4 demonstrated that the failure of the young infants to use form similarity was not due to insufficient processing time or the inability to discriminate between the individual X and O elements. The results suggest that different Gestalt principles may become functional over different time courses of development, and that not all principles are automatically deployed in the manner originally proposed by Gestalt theorists.

Learning Perceptual Organization in Infancy

It has been demonstrated that older infants (6- to 7-month-olds), but not younger infants (3- to 4-month-olds), use form similarity to organize stimuli consisting of X and O elements. We investigated whether utilization of form similarity is governed by maturation or experience by contrasting how infants perform when familiarized with a single exemplar versus multiple exemplars depicting a particular organization. In Experiment 1, 3- to 4-month-olds failed to organize alternating columns or rows of squares and diamonds or Hs and Is, respectively. In Experiment 2, same-aged infants familiarized with all three patterns (X-O, square-diamond, H-I) displayed evidence of organization. The results suggest that 3- to 4-month-olds can use form similarity to organize visual patterns in a concept-formation task. The findings imply that perceptual organization based on form similarity is learned through experience with multiple patterns depicting a common arrangement, rather than immediately apprehended in an individual pattern.

Progressive and regressive developmental changes in neural substrates for face processing: testing specific predictions of the Interactive Specialization account.

Face processing undergoes a fairly protracted developmental time course but the neural underpinnings are not well understood. Prior fMRI studies have only examined progressive changes (i.e., increases in specialization in certain regions with age), which would be predicted by both the Interactive Specialization (IS) and maturational theories of neural development. To differentiate between these accounts, the present study also examined regressive changes (i.e., decreases in specialization in certain regions with age), which is predicted by the IS but not maturational account. The fMRI results show that both progressive and regressive changes occur, consistent with IS. Progressive changes mostly occurred in occipital-fusiform and inferior frontal cortex whereas regressive changes largely emerged in parietal and lateral temporal cortices. Moreover, inconsistent with the maturational account, all of the regions involved in face viewing in adults were active in children, with some regions already specialized for face processing by 5 years of age and other regions activated in children but not specifically for faces. Thus, neurodevelopment of face processing involves dynamic interactions among brain regions including age-related increases and decreases in specialization and the involvement of different regions at different ages. These results are more consistent with IS than maturational models of neural development.

Contrast and the justification of effort

When humans are asked to evaluate rewards or outcomes that follow unpleasant (e.g., high-effort) events, they often assign higher value to that reward. This phenomenon has been referred to ascognitive dissonance or justification of effort. There is now evidence that a similar phenomenon can be found in nonhuman animals. When demonstrated in animals, however, it has been attributed to contrast between the unpleasant high effort and the conditioned stimulus for food. In the present experiment, we asked whether an analogous effect could be found in humans under conditions similar to those found in animals. Adult humans were trained to discriminate between shapes that followed a high-effort versus a low-effort response. In test, participants were found to prefer shapes that followed the high-effort response in training. These results suggest the possibility that contrast effects of the sort extensively studied in animals may play a role in cognitive dissonance and other related phenomena in humans.

Are Some Gestalt Principles Deployed More Readily than Others during Early Development? The Case of Lightness versus Form Similarity.

Four experiments investigated how readily infants achieve perceptual organization by lightness and form similarity. Infants were (a) familiarized with elements that could be organized into rows or columns on the basis of lightness or form similarity and tested with vertical versus horizontal bars depicting the familiar versus novel organization or (b) familiarized with bars and tested with elements. For lightness similarity, generalization occurred in both tasks; however, for form similarity, generalization occurred only in the elements --> bars task. The findings indicate that lightness similarity is more readily deployed than form similarity and are discussed in the context of (a) whether the difference reflects speed of application or experience-based learning, (b) evidence from visual agnosic patients and the time course of application of the principles in healthy adults, and (c) development of dorsal and ventral visual processing streams.

Race-based perceptual asymmetries underlying face processing in infancy.

Adults process other-race faces differently than own-race faces. For instance, a single other-race face in an array of own-race faces attracts Caucasians’ attention, but a single own-race face among other-race faces does not. This perceptual asymmetry has been explained by the presence of an other-race feature in other-race faces and its absence in own-race faces; this difference is thought to underlie race-based differences in face processing. We examined the developmental origins of this mechanism in two groups of Caucasian 9-month-olds. Infants in the experimental group exhibited a preference for a pattern containing a single Asian face among seven Caucasian faces over a pattern containing a single Caucasian face among seven Asian faces. This preference was not driven by the majority of elements in the images, because a control group of infants failed to exhibit a preference between homogeneous patterns containing eight Caucasian versus eight Asian faces. The results demonstrate that an other-race face among own-race faces attracts infants’ attention but not vice versa. This perceptual asymmetry suggests that the other-race feature is available to Caucasians by 9 months of age, thereby indicating that mechanisms of specialization in face processing originate early in life.

Visual pop-out in young infants : Convergent evidence and an extension

Abstract The familiarization/novelty-preference procedure was used to test for visual pop-out of two possible perceptual primitives, line-crossings and orientation differences, in 3- to 4-month-old infants. In Experiment 1, infants familiarized with an array consisting of either 25 + or L (or T) micropatterns subsequently preferred a test stimulus that contained a single novel micropattern among 24 familiar distractors when it was paired with a stimulus that contained a single familiar micropattern among 24 novel distractors. This result indicates that the discrepant and presumed pop-out element captured attention and directed infant looking. Experiment 2 revealed that an oblique among verticals (or vice versa) also elicited a pop-out effect. These findings provide convergent evidence of visual pop-out in young infants. They also indicate that, as in adults, pop-out of orientation differences in early infancy is engendered by coarse coding of lines into “tilted” versus “nontilted’ categories.

Neural Developmental Changes in Processing Inverted Faces

We explored developmental changes in neural substrates for face processing, using fMRI. Children and adults performed a perceptual-matching task with upright and inverted face and animal stimuli. Behaviorally, inversion disrupted face processing more than animal processing for adults and older children. In line with this behavioral pattern, the left middle occipital gyrus showed a stronger face than animal inversion effect in adults. Moreover, a superior aspect of this region showed a greater face inversion effect in older than in younger children, indicating a developmental change in the processing of inverted faces. The visual regions recruited for inverted face processing in adults also overlapped more with brain regions involved in the viewing of upright objects than with regions involved in the viewing of upright faces in an independent localizer task. Hence, when faces are inverted, adults recruit regions normally engaged for recognizing objects, possibly pointing to a role for the featural processing of inverted faces.