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Biomedical subjects

B J Knowlton

Publications and source records attributed to B J Knowlton.

At least 19 recordsLinked to original sources
PubMed2001

Hemispheric differences in object identification.

Although the right hemisphere is thought to be preferentially involved in visuospatial processing, the specialization of the two hemispheres with respect to object identification is unclear. The present study investigated the effects of hemifield presentation on object and word identification by presenting objects (Experiment 1) and words (Experiment 2) in a rapid visual stream of distracters. In Experiment 1, object images presented in the left visual field (i.e., to the right hemisphere) were identified with shorter display times. In addition, the left visual field advantage was greater for inverted objects. In Experiment 2, words presented in the right visual field (i.e., to the left hemisphere) under similar conditions were identified with shorter display times. These results support the idea that the right hemisphere is specialized with regard to object identification.

Attention↗
PubMed2000

Effects of US devaluation on win-stay and win-shift radial maze performance in rats.

Previous studies have shown double dissociations between win-stay and win-shift radial maze learning in terms of their underlying neural substrates. To examine the content of the associations formed in the two tasks, the authors devalued the food unconditioned stimulus (US) by taste aversion to differentiate stimulus-stimulus(CS-US) and stimulus-response (CS-CR) learning. US devaluation was performed in rats that were over- or undertrained on the win-stay task. Devaluation substantially reduced food consumption on the maze but failed to disrupt choice accuracy, regardless of the amount of training. Devaluation did not affect latency in overtrained rats but did increase latency in undertrained rats. In the win-shift task, devaluation caused rats to reject the reinforcer, yet they continued to accurately win-shift, but with significantly longer latencies (Experiment 3). The results suggest that an S-R association may mediate performance after extended win-stay training. In contrast, a US representation appears to be recalled during early win-stay and win-shift performance.

Animals↗
PubMed2000

Remembering episodes: a selective role for the hippocampus during retrieval.

Some memories are linked to a specific time and place, allowing one to re-experience the original event, whereas others are accompanied only by a feeling of familiarity. To uncover the distinct neural bases for these two types of memory, we measured brain activity during memory retrieval using event-related functional magnetic resonance imaging. We show that activity in the hippocampus increased only when retrieval was accompanied by conscious recollection of the learning episode. Hippocampal activity did not increase for items recognized based on familiarity or for unrecognized items. These results indicate that the hippocampus selectively supports the retrieval of episodic memories.

Adult↗
PubMed2000

Dissociating the effects of featural and conceptual interference on multiple target processing in rapid serial visual presentation.

Attentional blink (AB) describes the finding that, when subjects attend to a specified target in a rapidly presented visual stream, they show a decreased ability to process a subsequent probe item for up to 600 msec. In the present study, the roles of featural and conceptual interference in the processing of targets and probes in a rapid serial visual presentation stream were examined. In Experiment 1, featurally more complex T + 1 items produced larger AB even when the physical energy of the stimulus (e.g., the number of pixels) was held constant. In Experiment 2, the conceptual category of the T + 1 item affected target identification but not AB magnitude. These result suggest that featural interference is a major determinant of AB magnitude, whereas featural and conceptual interference both affect target identification.

Attention↗
PubMed2000

Long-term retinotopic priming in object identification.

An important result in perception research is that priming in an object naming task is invariant with translation and left-right reflection. A more sensitive object recognition paradigm was used in three experiments in order to investigate the extent to which priming of object identification is affected by changes in left-right orientation and position. In a prime phase, participants viewed consecutively presented object images. In a subsequent probe phase, participants identified familiar objects in rapid visual streams of nonobject distractors. In Experiment 1, images previously viewed in the same left-right orientation were primed more than images previously viewed in the opposite orientation (i.e., a left-right reflection). This reflection-sensitive priming was replicated in Experiment 2 using a brief (300-msec) prime exposure. In Experiment 3, when the retinal locations of prime and probe images matched, reflection-sensitive priming was also obtained, but when the retinal locations of prime and probe images differed, no reflection-sensitive priming was observed. These results suggest that a single prime exposure can produce long-term priming that is sensitive to left-right reflection, but that this priming is specific to a retinal location.

Adult↗
PubMed1998

The relationship between remembering and knowing: a cognitive neuroscience perspective.

Cognitive neuroscience has provided strong support for the idea that there are multiple memory systems. Recent evidence suggests that remembering and knowing may be two types of recognition with different neural substrates. The remember/know distinction is not equivalent to the explicit/implicit distinction because both remembering and knowing are impaired after damage to medial temporal lobe structures. A number of converging lines of evidence suggest that the relationship between remembering and knowing is one redundancy, with "knowing" processes also active during remembering. Remembering appears to depend additionally on frontal lobe functioning.

Amnesia↗
PubMed1996

A neostriatal habit learning system in humans.

Amnesic patients and nondemented patients with Parkinson's disease were given a probabilistic classification task in which they learned which of two outcomes would occur on each trial, given the particular combination of cues that appeared. Amnesic patients exhibited normal learning of the task but had severely impaired declarative memory for the training episode. In contrast, patients with Parkinson's disease failed to learn the probabilistic classification task, despite having intact memory for the training episode. This double dissociation shows that the limbic-diencephalic regions damaged in amnesia and the neostriatum damaged in Parkinson's disease support separate and parallel learning systems. In humans, the neostriatum (caudate nucleus and putamen) is essential for the gradual, incremental learning of associations that is characteristic of habit learning. The neostriatum is important not just for motor behavior and motor learning but also for acquiring nonmotor dispositions and tendencies that depend on new associations.

Aged↗
PubMed1996

Artificial grammar learning depends on implicit acquisition of both abstract and exemplar-specific information.

The contributions of exemplar-specific and abstract knowledge to artificial grammar learning were examined in amnesic patients and controls. In Experiment 1, grammatical rule adherence and chunk strength exerted separate effects on grammaticality judgments. Amnesic patients exhibited intact classification performance, demonstrating the same pattern of results as controls. In Experiment 2, amnesic patients exhibited impaired declarative memory for chunks. In Experiment 3, both amnesic patients and controls exhibited transfer when tested with a letter set different than the one used for training, although performance was better when the same letter sets were used at training and test. The results suggest that individuals learn both abstract information about training items and exemplar-specific information about chunk strength and that both types of learning occur independently of declarative memory.

Age Factors↗
PubMed1996

Dissociable properties of memory systems: differences in the flexibility of declarative and nondeclarative knowledge.

Amnesic patients (n = 8), who have severely impaired declarative memory, learned a probabilistic classification task at the same rate as normal subjects (n = 16) but subsequently were impaired on transfer tests that required flexible use of their task knowledge. A second group of controls (n = 20) rated the questions on the transfer tests according to whether the questions simply reinstated the training conditions or required flexible use of task knowledge. The amnesic patients tended to be impaired on the same items that were rated as requiring indirect or flexible use of knowledge. Thus, control subjects acquired declarative knowledge about the task that could be applied flexibly to the transfer tests. The nondeclarative memory available to amnesic patients was relatively inflexible and available only in conditions that reinstantiated the conditions of training. These findings show that declarative memory has different operating characteristics than nondeclarative memory.

Adult↗
PubMed1995

Learning about categories in the absence of memory.

A fundamental question about memory and cognition concerns how information is acquired about categories and concepts as the result of encounters with specific instances. We describe a profoundly amnesic patient (E.P.) who cannot learn and remember specific instances--i.e., he has no detectable declarative memory. Yet after inspecting a series of 40 training stimuli, he was normal at classifying novel stimuli according to whether they did or did not belong to the same category as the training stimuli. In contrast, he was unable to recognize a single stimulus after it was presented 40 times in succession. These findings demonstrate that the ability to classify novel items, after experience with other items in the same category, is a separate and parallel memory function of the brain, independent of the limbic and diencephalic structures essential for remembering individual stimulus items (declarative memory). Category-level knowledge can be acquired implicitly by cumulating information from multiple training examples in the absence of detectable conscious memory for the examples themselves.

Aged↗
PubMed1995

Remembering and knowing: two different expressions of declarative memory.

Amnesic patients and a control group were given a recognition test 10 min after studying words. For each recognized word, participants indicated whether they remembered it (R) or whether simply they knew that the word was presented but had no recollections about it (K). The patients were impaired for both R and K responses, performing like a control group tested after 1 week. Another control group was tested both 10 min and 1 week after study. The proportion of words initially eliciting an R response and later eliciting a K response exceeded the proportion of K responses that shifted to R responses. These data are accounted for if items initially eliciting R responses can also elicit K responses. We conclude that the R-K distinction does not reflect the operation of explicit and implicit memory but reflects instead a distinction within declarative memory. Thus, K responses depend on brain structures damaged in amnesia; R responses depend on these same structures and also on the frontal lobes for contextual information.

Aged↗
PubMed1994

The information acquired during artificial grammar learning.

In an artificial grammar learning task, amnesic patients classified test items as well as normal subjects did. Item similarity did not affect grammaticality judgments when similar and nonsimilar test items were balanced for the frequency with which bigrams and trigrams (chunks) that appeared in the training set also appeared in the test items. Amnesic patients performed like normal subjects. The results suggest that concrete information about letter chunks can influence gramaticality judgments and that this information is acquired implicitly. The similarity of whole test items to training items does not appear to affect grammaticality judgments.

Aged↗
PubMed1993

The learning of categories: parallel brain systems for item memory and category knowledge.

A fundamental question about cognition concerns how knowledge about a category is acquired through encounters with examples of the category. Amnesic patients and control subjects performed similarly at classifying novel patterns according to whether they belonged to the same category as a set of training patterns. In contrast, the amnesic patients were impaired at recognizing which dot patterns had been presented for training. Category learning appears to be independent of declarative (explicit) memory for training instances and independent of the brain structures essential for declarative memory that are damaged in amnesia. Knowledge about categories can be acquired implicitly by cumulating information from multiple examples.

Aged↗
PubMed1993

Projections from the auditory cortex to the pontine nuclei in the rabbit.

The pontine projection from the auditory cortex was studied in 24 New Zealand albino rabbits using the method of anterograde transport of HRP-WGA. Microinjections of HRP-WGA (0.03-0.1 microliter) were made in the auditory cortex, which was located by electrophysiological criteria. The auditory cortex was shown to project ipsilaterally to ventral and lateral regions in the caudal pontine nuclei, and to the dorsolateral pontine nuclei in more rostral sections. Labeled terminals were also occasionally seen in the caudal medial pontine nuclei. These results suggest that the auditory cortex can modulate cerebellar input from caudal regions of the pontine nuclei, which project to cerebellar regions shown to be important for classical conditioning.

Animals↗
PubMed1993

Dissociation of kainic acid lesion effects on the asymmetry of rotation and lateral head movements.

The present study tested the relationship between horizontal head movement asymmetry and rotation behavior after unilateral kainic acid (KA) lesions of the pontine reticular formation (PRF). In line with previous studies, the lesions decreased the rate of ipsilateral spontaneous head movements and spared contralateral spontaneous head movements. In contrast to previous studies, however, these lesions facilitated ipsilateral rather than contralateral rotation. Histological analysis revealed that the ipsilateral rotation may be accounted for by distant effects of the KA injection in the PRF on the ipsilateral substantia nigra (SN). We conclude that unilateral lesions consisting solely of the PRF lead to a preference for contralateral horizontal head movements which then channel rotated away from the lesioned side. KA injections in the PRF, however, are also associated with distant lesions within the ipsilateral extrapyramidal system which override the channeling effect of the contralateral head movements and induce instead ipsilateral rotation.

Animals↗
PubMed1992

Conditioning using a cerebral cortical conditioned stimulus is dependent on the cerebellum and brain stem circuitry.

Electrical stimulation of the auditory cortex (AC) was used as a conditioned stimulus (CS) in the rabbit conditioned eyeblink preparation to trace the functional anatomical connections between the AC and the circuitry underlying this conditioned response. Conditioning was shown to be dependent on the cerebellar interpositus nucleus and the pontine nuclei (PN), structures that are essential for conditioning using a peripheral CS. The results suggest that the cerebellum and associated brain stem circuitry are a necessary part of the memory trace circuit for the conditioned eyeblink response, even when the cerebral cortex is artifically engaged as a CS by electrical stimulation. The results also suggest that the PN are a site of convergence between the CS circuit subserving classical conditioning for peripheral stimuli and the AC, and may therefore be a site where the AC can modulate more elaborate forms of conditioning.

Animals↗
PubMed1989

Stimulation of the lateral septum is a more effective conditioned stimulus than stimulation of the medial septum during classical conditioning of the eye-blink response.

Eight rabbits were trained in the classically conditioned eye-blink response procedure using stimulation of the septal nuclei as the conditioned stimulus (CS). Each rabbit was trained with both medial septal stimulation and lateral septal stimulation. Stimulation of the medial septum was a far less effective CS than stimulation of the lateral septum. This effect may be due to the different roles of these two nuclei in classical conditioning. Conditioning using lateral septal stimulation as a CS is dependent on the cerebellar interpositus nucleus as is conditioning using peripheral and other brain stimulation CSs.

Animals↗