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PubMed1984

Conceptual masking: the effects of subsequent visual events on memory for pictures.

Three experiments studied the effects of voluntary and involuntary focus of attention on recognition memory for pictures. Experiments 1 and 3 tested the conceptual-masking hypothesis, which holds that a visual event will automatically disrupt processing of a previously glimpsed picture if that event is new and meaningful. Memory for 112-ms pictures was tested under conditions where the to-be-ignored 1.5-s interstimulus interval contained a blank field; a repeating picture; a new picture; a new, nonsense picture; or a new, inverted picture each time. The blank field, repeating picture, and new, nonsense picture did not disrupt memory as much as a new, meaningful picture, supporting the conceptual-masking hypothesis. Experiment 2 studied voluntary attentional control of encoding by instructing subjects to focus attention on the brief pictures, all pictures, or the long pictures in a sequence. Recognition memory for pictures of both durations showed a striking ability of observers to process pictures selectively. The possible role of these effects in visual scanning are discussed.

Adult↗
PubMed2005

Dissociation between ventral and dorsal fMRI activation during object and action recognition.

Neuropsychological case studies suggest the existence of two functionally separate visual streams: the ventral pathway, central for object recognition; and the dorsal pathway, engaged in visually guided actions. However, a clear dissociation between the functions of the two streams has not been decisively shown in intact humans. In this study, we demonstrate dissociation between dorsal and ventral fMRI activation patterns during observation of object manipulation video clips. Parietal areas, such as anterior intraparietal sulcus (aIPS) display grasp viewing-dependent adaptation (i.e., fMR adaptation during repeated viewing of the same object-grasping movement) as well as a contralateral preference for the viewed manipulating hand. Ventral regions, such as the fusiform gyrus, show similar characteristics (i.e., adaptation, contralateral preference), but these depend on object identity. Our results support the hypothesized functional specialization in the visual system and suggest that parietal areas (such as aIPS) are engaged in action recognition, as well as in action planning.

Adult↗
PubMed2003

Competition and selection during visual processing of natural scenes and objects.

When a visual scene, containing many discrete objects, is presented to our retinae, only a subset of these objects will be explicitly represented in visual awareness. The number of objects accessing short-term visual memory might be even smaller. Finally, it is not known to what extent "ignored" objects (those that do not enter visual awareness) will be processed--or recognized. By combining free recall, forced-choice recognition and visual priming paradigms for the same natural visual scenes and subjects, we were able to estimate these numbers, and provide insights as to the fate of objects that are not explicitly recognized in a single fixation. When presented for 250 ms with a scene containing 10 distinct objects, human observers can remember up to 4 objects with full confidence, and between 2 and 3 more when forced to guess. Importantly, the objects that the subjects consistently failed to report elicited a significant negative priming effect when presented in a subsequent task, suggesting that their identity was represented in high-level cortical areas of the visual system, before the corresponding neural activity was suppressed during attentional selection. These results shed light on neural mechanisms of attentional competition, and representational capacity at different levels of the human visual system.

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PubMed1983

Multimodality evoked potentials and neurophysiological tests in multiple sclerosis. Effects of hyperthermia on test results.

Data on critical frequency of photic driving (CFPD), frequency following response (FFR), and visual, somatosensory (peroneal nerve), and brain-stem auditory evoked potentials (EPs) were obtained from 20 patients who had clinically definite multiple sclerosis and ten healthy normal subjects in a controlled, balanced study under normothermic and hyperthermic (+1 degrees C) conditions with a test-retest interval of one week. Normal subjects' test results showed no changes during hyperthermia. Patients' EP and CFPD data correlated well with history, clinical signs, and symptoms during both normothermia and hyperthermia. The FFR test data were equivocal and not fully analyzed. Data from the four other tests showed additional patient abnormalities during hyperthermia. Multimodality testing increased the number of patient abnormalities compared with single tests, and the number increased further during hyperthermia. Test-retest reproducibility was higher during hyperthermia.

Adult↗
PubMed1985

The flight of colors test in multiple sclerosis.

Flight of colors (FOC), the rapidly changing series of colored afterimages perceived when a bright light briefly strikes the eye, is impaired or absent in patients with lesions affecting central visual fields, especially optic neuropathies (ONs). The effectiveness of a bedside test of FOC using a pocket flashlight was compared with that of pattern-reversal visual evoked responses (PRVERs) in examining 74 subjects): 20 controls, seven patients with ON not due to multiple sclerosis (MS), 26 patients with MS, and 21 patients with possible MS and no clinical ON. The FOC test correctly identified 95 of 99 normal eyes and 45 of 49 eyes with ON, and accurately diagnosed 140 (95%) of 148 eyes overall. In 84 eyes examined by PRVER and FOC, the results agreed in 73 cases (87%), including those of subclinical ON.

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