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At least 1,207 records · Page 67Linked to original sources
PubMed1982

Effect of task demands on dual coding of pictorial stimuli.

Recent studies have suggested that verbal labeling of a picture does not occur automatically. Although several experiments using paired-associate tasks produced little evidence indicating the use of a verbal code with picture stimuli, the tasks were probably not sensitive to whether the codes were activated initially. It is possible that verbal labels were activated at input, but not used later in performing the tasks. The present experiment used a color-naming interference task in order to assess, with a more sensitive measure, the amount of verbal coding occurring in response to word or picture input. Subjects named the color of ink in which words were printed following either word or picture input. If verbal labeling of the input occurs, then latency of color naming should increase when the input item and color-naming word are related. The results provided substantial evidence of such verbal activation when the input items were words. However, the presence of verbal activation with picture input was a function of task demands. Activation occurred when a recall memory test was used, but not when a recognition memory test was used. The results support the conclusion that name information (labels) need not be activated during presentation of visual stimuli.

Attention↗
PubMed1992

Columns for visual features of objects in monkey inferotemporal cortex.

At early stages of the mammalian visual cortex, neurons with similar stimulus selectivities are vertically arrayed through the thickness of the cortical sheet and clustered in patches or bands across the surface. This organization, referred to as a 'column', has been found with respect to one-dimensional stimulus parameters such as orientation of stimulus contours, eye dominance of visual inputs, and direction of stimulus motion. It is unclear, however, whether information with extremely high dimensions, such as visual shape, is organized in a similar columnar fashion or in a different manner in the brain. Here we report that the anterior inferotemporal area of the monkey cortex, the final station of the visual cortical stream crucial for object recognition, consists of columns, each containing cells responsive to similar visual features of objects.

Animals↗
PubMed2001

Unsupervised statistical learning of higher-order spatial structures from visual scenes.

Three experiments investigated the ability of human observers to extract the joint and conditional probabilities of shape co-occurrences during passive viewing of complex visual scenes. Results indicated that statistical learning of shape conjunctions was both rapid and automatic, as subjects were not instructed to attend to any particularfeatures of the displays. Moreover, in addition to single-shape frequency, subjects acquired in parallel several different higher-order aspects of the statistical structure of the displays, including absolute shape-position relations in an array, shape-pair arrangements independent of position, and conditional probabilities of shape co-occurrences. Unsupervised learning of these higher-order statistics provides support for Barlow's theory of visual recognition, which posits that detecting "suspicious coincidences" of elements during recognition is a necessary prerequisite for efficient learning of new visual features.

Adult↗
PubMed1995

A computational model for the neurobiological substrates of visual attention.

Two interesting and complex tasks are performed by the brain in the process of perception: the integration of characteristics leading to an easier recognition of a pattern as a whole (binding), and the extraction of properties that need to be detailed and analyzed (attention). Attention seems to have a reciprocal relation with binding, inasmuch as the latter promotes the composition of features and their dependencies, while the former selects a single characteristic independently of the remainder. Classically, binding is viewed as a process whereby sets of properties are gathered in representative entities, which are themselves linked to form higher level structures, in a sequence that culminates in the total integration of the pattern features in a localized construct. The convergent axonal projections from one cortical area to another would be the neurobiological mechanism through which binding is achieved. Attention comprises the selective excitation of neuronal networks or pathways that stand for specific pattern properties. The thalamus and its reticular nucleus would then be the anatomical substrate of the attentional focus. In this paper we propose a computational model aiming at bringing together the main (and apparently diverging) ideas about binding and attention. Based on experimental data, a neuronal network representing cortical pyramidal cells is assembled, and its structure and function are related to the binding and attention phenomena. Actually, the convergent projections that enlarge the visual receptive field are associated to binding, while a specific change in the pyramidal cell behavior is responsible for attention. Computer simulations are shown which reproduce the electrophysiology of pyramidal cells and mimic some interesting experimental results in visual attention. We conclude by conjecturing that attention is a driven interruption in the regular process of binding.

Algorithms↗
PubMed1991

Effects of encoding the perceptual features of pictures on memory.

Four experiments investigated whether manipulations of type of encoding affects the likelihood of remembering pictures' visual details and their names. Using an incidental learning procedures, subjects were led to make judgments about pictures' colors, spatial orientations, or appropriateness in a scene. The results indicate that the nature of the memory test influences the effectiveness of different encoding conditions. Recall and recognition of pictures' names were best after subjects judged scene encodings, second best after they judged orientation, and poorest after they judged color. However, the results for the recognition of pictures' visual details were quite different. Analyses of d' suggested that type of encoding task had no effect on memory for visual details, whereas analysis of Pr (hit rate minus false-alarm rate) suggested that memory for visual details was impaired by conceptual encoding (judging the appropriateness of a picture in a scene). The results of one experiment demonstrated that these findings were not produced by variation in distinctiveness of the encoding questions. This pattern of findings implies that conceptual encoding facilitates retention of the names of the pictures at the cost of some loss in the ability to retain specific visual details.

Adult↗
PubMed2004

Right hemisphere superiority for subitising.

Lateral differences in the enumeration of small sets of items (i.e., between two and five) were investigated in a normal adult sample. Confounds due to stimulus repetition, which have characterised previous subitising research, were eliminated in a task involving the presentation of purely random item arrays to the left and right visual fields. The results indicated a clear left visual field advantage for the enumeration of arrays containing three to four items. This finding is consistent with the widely held view that the subitising process is used to enumerate arrays of up to four items, and calls into question Butterworth's (1999) recent claim that subitising is a left hemisphere process. The implications for previous pattern recognition and visual process accounts of this ability are considered.

Adult↗
PubMed1989

A case of associative visual agnosia: neuropsychological findings and theoretical considerations.

A 61-year-old right-handed man fell downstairs and was found unconscious. There was no abnormality in the general physical examinations. Neurological examinations revealed a quadrantanopia. Neuropsychological examination revealed an impairment in recent verbal memory, alexia, agraphia, object agnosia, color naming difficulty, prosopagnosia, and visuospatial constructional disability. CT scan demonstrated subcortical hematomas in the temporo-occipital regions of both hemispheres. MRI demonstrated extensive low-intensity lesions in the lingual, fusiform and posterior inferior temporal gyri on both hemispheres. Both inferior longitudinal fasciculi were also affected. His neuropsychological deficits seem best described as a typical form of associative visual agnosia. From the results of neuroradiological findings, the authors emphasize that associative visual agnosia might be produced by an intrahemispheric disconnection between the visual cortices and the temporal lobes which are supposed to be the storage site of the engrams of visual memories. Moreover, the neuropsychological findings suggest that the visuo-constructional ability to convert the two-dimensional input to the three-dimensional construction and the capacity of three-dimensional imagination were severely impaired in our patient. It was considered that these neuropsychological features play an important role in the recognition difficulties of associative visual agnosia.

Agnosia↗
PubMed1991

Visual recognition memory. Neurophysiological evidence for the role of temporal white matter in man.

A novel event-related potential (ERP) elicited by a visuospatial recognition memory task was recorded in 20 patients with temporal lobe epilepsy using depth electrodes sited in the temporal lobes. The ERPs comprised two components, an N400 and a P600, and were similar in morphology to the previously reported ERP to verbal recognition memory tasks. The two ERP components in both verbal and visuospatial tasks were dependent on stimulus type and our data suggest that they do not simply represent delayed P300 ERP responses. In 17/20 patients robust, reliable bilaterally present ERPs were elicited by both verbal and visuospatial memory tasks. N400 amplitude was larger in response to novel stimuli, whereas P600 amplitude was larger to repeated stimuli. P600 amplitude was larger in the right temporal lobe to both visuospatial and verbal stimulus material. N400 and P600 latencies did not vary with task, stimulus type or side of recording. In 3/20 patients, no ERPs were elicited by either memory task. In all 3 cases, unilateral temporal white matter abnormalities were demonstrated by magnetic resonance imaging. Behavioural measures, expressed in the form of standardized accuracy scores, did not differ from those of a normal control group, and hence are unlikely to account for the abnormalities in ERPs. These results are discussed with reference to the primate visual recognition memory pathway and suggest that ERPs to recognition memory tasks are generated by an interaction between the two homologous inferotemporal recognition memory pathways.

Adult↗
PubMed1984

Evoked potentials in Huntington's disease. A comparative and longitudinal study.

Pattern-reversal visual (PRVEPs), brain-stem auditory (BAEPs), and somatosensory (SSEPs) evoked potentials were studied in 12 patients with Huntington's disease (HD) and were repeated in eight at one and two years. The mean cortical SSEP amplitude was decreased compared with that of age-matched controls, with a trend of decreasing amplitude with increasing duration and severity of illness. The SSEP latency was not significantly different from that of controls. The PRVEPs and BAEPs were normal. The serial studies showed a progressive decrease in amplitude of the SSEP over a two-year period. These neurophysiological findings may reflect the pathological involvement of the thalamus reported for HD. While evoked potentials are not of use in individual case diagnosis, the SSEP may be an objective physiological method for following the course of the disease in HD and the effects of therapeutic intervention in patient populations.

Aged↗
PubMed2006

Multifocal visual evoked potential latency analysis: predicting progression to multiple sclerosis.

OBJECTIVE: To monitor the difference in conversion rates to multiple sclerosis (MS) in 46 patients with optic neuritis between patients with multifocal visual evoked potential latency delay and those with normal latency. DESIGN: Prospective case series. SETTING: Metropolitan neuro-ophthalmology clinic. PARTICIPANTS: Forty-six patients with optic neuritis who did not have a diagnosis of MS on enrollment in the study. MAIN OUTCOME MEASURES: Conversion to MS according to the McDonald criteria. RESULTS: Analysis revealed that only 22 subjects had multifocal visual evoked potential latency delay. Over 1 year, 36.4% of patients with optic neuritis with latency delays progressed clinically to MS compared with 0% of those with normal latencies (P = .03, chi2). CONCLUSION: This may indicate that multifocal visual evoked potential latency delay can assist in predicting progression to future MS.

Analysis of Variance↗
PubMed1991

Visual evoked potentials and visual prognosis following perinatal asphyxia.

Twenty-five children born at term with perinatal asphyxia were studied at age 2.5 to 4.5 years to evaluate visual function and to determine the prognostic value of postnatal assessments of visual outcome. Postnatal assessments included several visual evoked potentials and electroretinograms in the first week of life. Follow-up assessments included flash and pattern visual evoked potentials, visual evoked potential threshold measurements, and clinical eye examinations. Nineteen children had normal visual function, three were visually impaired, and three remained blind. A strong association was found between normal, abnormal, or absent visual evoked potentials in the early postnatal period and long-term visual outcome (P less than .0001). Other perinatal indicators of asphyxia, including neurologic status, Apgar scores, and arterial pH values, were poor predictors of visual outcome. The risk of visual impairment was limited to those survivors with neurodevelopmental deficits.

Asphyxia Neonatorum↗