Biomedical subjects

R S Bhatt

Publications and source records attributed to R S Bhatt.

At least 19 recordsLinked to original sources

PubMed2001

Dissociations between featural versus conjunction-based texture processing in infancy: analyses of three potential contributing factors.

Many models of object perception posit that adults encode individual features in visual scenes before processing the conjunction relations among these features to generate holistic representations. Prior research suggests that infants detect textural discrepancies based on individual features more readily than those based on feature conjunctions. While these results suggest adult-like qualitative differences in infants' processing of features versus conjunctions, there are potential alternative explanations. We examined three such explanations: (1) failure to process one of the features that constitute the conjunction, (2) failure to encode and remember conjunction information that is necessary to detect conjunction-based textural discrepancies, and (3) the fact that conjunction-based discrepancies involve stimuli that are more similar to original stimuli than those involving feature-based discrepancies. None of these factors could explain 5.5-month-olds' superior processing of featural than conjunction-based textural discrepancies. Thus, in infancy, as in adulthood, features and conjunction relations appear to be processed by qualitatively different mechanisms.

Child Development↗

PubMed2001

Object recognition and object segregation in infancy: historical perspective, theoretical significance, "kinds" of knowledge, and relation to object categorization.

Needham (2001, this issue) reports that 4.5-month-old infants can use a short-term familiarization experience with a single object to facilitate the segregation of a visual display consisting of a configurally similar object and a configurally dissimilar adjacent object. We reflect on this finding in the larger context of Needham's systematic research on the development of object perception, a program that has included (1) a series of empirical studies designed to identify the different cues that infants use for object segregation and (2) a theoretical framework in which infants are presumed to integrate these cues to form interpretations of complex visual displays.

Child Development↗

PubMed2001

Pictorial cues and three-dimensional information processing in early infancy.

Adults derive 3-D information from 2-D images by initially processing local line junction cues and then combining information from many junctions. Prior research indicates that 3-month-olds are sensitive to 3-D cues in individual line junctions. In Experiment 1, we examined whether infants are sensitive to holistic combinations of line junctions that adults use to derive overall 3-D structure. Infants detected a misoriented shape in an array depicting 3-D blocks but not in 2-D patterns that contained all of the trilinear junctions of the 3-D shapes but without the connecting lines. Thus, like adults, infants exhibited sensitivity to holistic combinations of line junctions rather than to individual junctions. In Experiment 2, when confronted with two test patterns, one containing an individual novel element among 15 familiar elements and the other containing a single familiar element among 15 novel elements, infants preferred to look at the former pattern in the 3-D condition but at the latter pattern in the 2-D condition. Thus, akin to pop-out in adults, discrepancies in 3-D cues selectively engaged infants' attention. These results suggest that 3-month-olds are not only sensitive to holistic combinations of line junctions that adults use to derive 3-D information but also selectively attend to these 3-D cues in static images.

Analysis of Variance↗

PubMed2001

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.

Animals↗

PubMed2000

Discoidin domain receptor 1 functions in axon extension of cerebellar granule neurons.

In the developing cerebellum, granule neuron axon outgrowth is a key step toward establishing proper connections with Purkinje neurons, the principal output neuron of the cerebellum. During a search for genes that function in this process, we identified a receptor tyrosine kinase discoidin domain receptor 1 (DDR1) expressed in granule cells throughout their development. Overexpression of a dominant-negative form of DDR1 in immature granule cells results in severe reduction of neurite outgrowth in vitro, in dissociated primary culture, and in vivo, in organotypic slices of neonatal cerebellum. Granule cells that fail to extend axons are positive for differentiation markers such as TAG-1 and the neuron-specific class III beta-tubulin, suggesting that development is affected after granule cells commit to terminal differentiation. DDR1 activation appears to be mediated by its ligand, collagen, which is localized to the pial layer of the developing cerebellum, thereby leading to granule cell parallel fiber extension. Our results therefore indicate that collagen-DDR1 signaling is essential for granule neuron axon formation and further suggest a unique role of pia in cerebellar cortex histogenesis.

Animals↗

PubMed1999

Rapid detection of the mecA gene in methicillin resistant staphylococci using a colorimetric cycling probe technology.

A Cycling Probe Technology (CPT) assay was developed for the detection of the mecA gene from methicillin resistant staphylococcal cultures. The assay is based on a colorimetric enzyme-immuno-assay (EIA) and uses a mecA probe (DNA-RNA-DNA) labeled with fluorescein at the 5'-terminus and biotin at the 3'-terminus. The reaction occurs at a constant temperature that allows the target DNA to anneal to the probe. RNase H cuts the RNA portion, allowing the cut fragments to dissociate from the target, making it available for further cycling. CPT-EIA uses streptavidin-coated microplate wells to capture uncut probe followed by detection with horseradish-peroxidase conjugated anti-fluorescein antibody. The assay was compared to PCR and shown to accurately detect the presence or absence of the mecA gene in 159 staphylococcal clinical isolates. The CPT-EIA assay takes two hours starting from cultured cells compared with the 24-48 h required for detection of methicillin resistance by conventional susceptibility tests.

Bacterial Proteins↗

PubMed1999

A mouse serine/threonine kinase homologous to C. elegans UNC51 functions in parallel fiber formation of cerebellar granule neurons.

The formation of the cerebellar circuitry depends on the outgrowth of connections between the two principal classes of neurons, granule neurons and Purkinje neurons. To identify genes that function in axon outgrowth, we have isolated a mouse homolog of C. elegans UNC51, which is required for axon formation, and tested its function in cerebellar granule neurons. Murine Unc51.1 encodes a novel serine/threonine kinase and is expressed in granule cells in the cerebellar cortex. Retroviral infection of immature granule cells with a dominant negative Unc51.1 results in inhibition of neurite outgrowth in vitro and in vivo. Moreover, infected neurons fail to express TAG-1 or neuron-specific beta-tubulin, suggesting that development is arrested prior to this initial step of differentiation. Thus, Unc51.1 signals the program of gene expression leading to the formation of granule cell axons.

Amino Acid Sequence↗

PubMed1998

Developmental changes in the specificity of memory over the first year of life.

In two experiments with 260 infants between 2 and 12 months of age, we examined how differences between the conditions of encoding and retrieval affect retention. Initially, 9- and 12-month-olds were tested with a different cue (Experiment 1) or in a different context (Experiment 2) after delays spanning their respective forgetting functions. These data were then combined with corresponding data previously collected from 2-to 6-month-olds trained and tested in an equivalent task. The resulting analyses revealed that the specificity constraints on memory retrieval become progressively looser at the extremes of the forgetting function with age. With increasing age, retention was less affected by cue changes after shorter absolute delays and, except at 6 months, by context changes after longer absolute delays. This pattern dovetails with evidence of decreasing specificity in the retrieval cues required for deferred imitation during infants' 2nd year and reveals that the memory abilities of older children evolve gradually from early in infancy.

Age Factors↗

PubMed1998

Perception of three-dimensional cues in early infancy.

Three experiments examined infants' processing of 3D information in static images. Three-month-olds familiarized with micropatterns that appeared to adults to be 3D blocks illuminated from the top subsequently preferred a test array that contained a micropattern that appeared to be a block illuminated from the bottom; however, they failed to detect comparable discrepancies in 2D images. Thus, 3-month-olds are sensitive to 3D cues in static images. In another experiment, infants failed to exhibit a preference between an array containing a single novel element among familiar elements and another array containing a single familiar element among novel elements. Thus, unlike discrepancies in fundamental features such as line-crossings, discrepancies in 3D cues failed to pop-out and engage infants' attention. These results reveal that 3-month-olds are sensitive to 3D cues in static images. However, discrepancies based on these cues may not engage infants' attention like those based on fundamental features.

Age Factors↗

PubMed1998

The ontogeny of long-term memory over the first year-and-a-half of life.

This research documents the development of long-term memory in human infants from 2 months through the end of the first year-and-a-half of life. In the initial study phase, we trained 6- to 18-month-old human infants in an operant task and tested them after increasing delays until they exhibited no retention for 2 successive weeks. In the second phase, their data were combined with data previously obtained from 2- to 6-month-olds in an equivalent task. The resulting function revealed that the duration of retention increases monotonically between 2 and 18 months of age. This increase was not due to age differences in original learning. This is the first systematic analysis of the course of long-term memory across an extended period of infant development that is based on standardized parameters of training and testing. It provides a reference function against which measures of retention from infants of different ages that are obtained in different memory tasks with different parameters can be meaningfully compared.

Age Factors↗

PubMed1997

Dissociation between features and feature relations in infant memory: effects of memory load.

Four experiments examined the effects of the number of features and feature relations on learning and long-term memory in infants. Three-month-olds learned to activate a mobile composed of either two or three kinds of blocks that differed in color, the figures displayed on them, and the figures' colors. Twenty-four hours later, infants trained with two objects discriminated feature recombinations but those trained with three objects did not. Even infants trained with three objects discriminated novel features, however, indicating that they remembered the individual features but not the relations among them. A subsequent experiment revealed that this dissociation between features and relations was induced by differential accessibility to memory rather than an encoding failure. We conclude that the size of the memory load selectively constrains infants' long-term memory for relational information. These results suggest that in infancy, as in adulthood, features and relations are psychologically distinct and that memory organization parallels the organization of perceptual processing.

Association Learning↗

PubMed1996

Set size, novelty, and visual pop-out in infancy.

The effects of set size and novelty on visual pop-out in 6-month-old infants was assessed in a perceptual-identification (memory reactivation) paradigm in which infants, trained and tested in their own homes, viewed a mobile containing a unique novel or familiar object amidst different numbers of familiar or novel distractors, respectively. Unique objects of both types popped out at all set sizes except the largest, where there was modest evidence that familiar distractors speeded processing (Experiment 1). When the proportion of familiar targets in a display of intermediate set size was increased, however, infants no longer detected the familiar target (Experiment 2). These findings offer additional support for the proposition that visual pop-out in infants and adults is the some phenomenon.

Adult↗

PubMed1996

Infants' forgetting of correlated attributes and object recognition.

Infants as young as 3 months of age can encode the relations among object features. Because object recognition depends critically upon a match between perceived feature configurations and representations of the object in long-term memory, the present experiments focused on infants' long-term memory for feature correlations. In 3 experiments with 72 3-month-olds, we documented the forgetting functions of different feature correlations, examined their relation to infants' memory for individual features, and replicated the findings with different stimuli. Infants were trained to activate a mobile composed of two kinds of blocks that differed in color, the figures displayed on them, and the figures' colors and were tested after different delays with recombinations of either the block colors, the figures, or the figure colors. Infants remembered some of the original feature combinations for up to 3 days but forgot all of them after 4 days. Even after 4 days, however, infants remembered the individual features that had entered into the original combinations. These results demonstrate that very young infants not only encode the relations among object features but also remember them for several days. Moreover, there is a dissociation in memory between features and feature relations: Feature relations are forgotten sooner than the individual features that comprise those relations.

Association Learning↗

PubMed1995

Developmental changes in the contextual control of recognition.

In three experiments, we explored potential developmental differences in the contextual control of target recognition using elementary perceptual features that differed only in their spatial relations. Three- and 6-month-old infants were trained in the presence of black horizontal and vertical line segments arranged as Ls, Ts, or +s on a pink background and were tested in the presence of the same line segments in a different spatial arrangement. At both ages, target recognition required a match between the primitive perceptual features in the test context and those present during training. Delayed recognition by younger but not older infants also required a match between specific spatial arrangements of the horizontal and vertical segments (+s versus Ls or Ts), despite the fact that infants of both ages had initially encoded these relations. These data suggest that by 6 months, spatial information in the periphery is detected preattentively via a parallel-processing mechanism, as it is in children and adults.

Age Factors↗

PubMed1994

Global and local processing of incidental information and memory retrieval at 6 months.

In five experiments, we examined the role of global and local cues in memory retrieval in infancy. Six-month-old infants were trained at home in a distinctive context (playpen liner) to kick to move a mobile. The liners were yellow and displayed either green stripes, green squares aligned vertically in stripe-like columns, or green squares in a grid pattern. The stripes and columns liners had a similar global configuration but different local components; the columns and grid liners had identical local components but different global configurations. When infants were tested 24 h after training in the presence of context liners that differed from the training context in either global configurations or local features, their memory retrieval was disrupted (Experiments 1 and 2). However, a change from stripes to columns failed to disrupt memory retrieval, even though the reverse change, from columns to stripes, did. Experiments 3, 4, and 5 revealed that this asymmetry was due to the fact that, when discriminative local information is not directly associated with training, a postperceptual strategy enables infants to disregard a mismatch in local information between training and test contexts and to generalize on the basis of a match in global information during the 24-h retention test. Thus, infants encode and remember for substantial periods of time both global configuration information and local component information in the incidental context in which an event occurs and flexibly utilize this information when responding to new events.

Color Perception↗

PubMed1992

Concept learning by monkeys with video picture images and a touch screen.

Two rhesus monkeys were trained in a same/different task to discriminate digitized computer-stored picture stimuli. The pictures were digitized from 35-mm slides and presented in pairs on a computer monitor. The monkeys were required to touch the pictures and then make a choice response to indicate whether the pictures were identical or nonidentical. The response areas and stimuli were located to the sides of the picture stimuli. Responses were defined and monitored by an infrared matrix touch screen. After learning the same/different task, both monkeys showed performance accuracy with novel picture stimuli similar to that with training picture stimuli. This accurate novel-picture transfer indicates that a same/different concept had been learned, a concept similar to the one they had previously demonstrated in a different apparatus with rear-projected slide stimuli and a response lever.

Animals↗

PubMed1989

Secondary generalization and categorization in pigeons.

In Experiment 1, one group of pigeons learned to classify a set of stimuli into the human language classes cat, flower, car, and chair (categorization); another group learned to classify the same set into arbitrary classes (pseudocategorization). Then, both groups were trained on a new categorization task and their performance compared to that of a control group that had no initial classification training. Hull's (1943) notion of secondary generalization (generalization that is not based on physical similarity but on mediating associations) predicts that categorization experience will facilitate the learning of a new categorization task, whereas pseudocategorization experience will impair it. However, in Experiment 1, performance on the new categorization task was not differently affected by prior experience. In Experiment 2, pigeons initially trained to classify a set of 48 stimuli (original training) were later trained to classify a subset of four of these stimuli using new responses (reassignment training). Then, they were tested on the 44 remaining stimuli. Performance better accorded with original than with reassignment training, indicating that categorization training did not lead to the formation of equivalence classes of stimuli, in which the equivalence relationship is mediated by secondary generalization. The lack of evidence of secondary generalization implies that our pigeons failed to meet Lea's (1984) criterion for conceptual behavior.

Journal Article↗

PubMed1987

Expression of a pseudogene for interferon-alpha L.

The human leukocyte interferon-alpha L (IFN-alpha L) appears to be a pseudogene because it contains a termination codon in the DNA coding for the precursor peptide (signal peptide), but the remainder of the gene codes for an interferon protein of normal length. To determine if this gene codes for an active interferon molecule, an expression plasmid was constructed for IFN-alpha L that was produced in Escherichia coli. The IFN-alpha L is active on human and bovine cells, and exhibits a trace of activity on mouse cells.

Cloning, Molecular↗