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PubMed1991

Perception of visual letter strings in a case of left neglect: manipulation of the word form.

Patients with lesions in the right parietal lobe neglect the left side of nonwords much more than the left side of words. This has been interpreted in terms of a more automatic process in reading words. The case of a patient with left visual neglect after a vascular right parietooccipital lesion is presented. He showed the phenomenon of a word superiority effect over nonword in reading at the beginning in a clinical test with static cards; 6 months later, after some recovery, the same phenomenon could be demonstrated only with tachistoscopic presentation, and it occurred even inside the good right visual hemifield. The word form of visually presented stimuli was manipulated, showing that there was a striking effect particularly when spacing the letters of words in a task that requires naming the stimulus. The patient's performance is interpreted in terms of an attentional deficit occurring at an early level of spatial information processing.

Attention↗
PubMed2006

Visuomotor priming of a manual reaching movement during a perceptual decision task.

This paper deals with the mental simulation of manual movement that sometimes accompanies the visual perception of an object. Previous studies investigated how visual objects prime the grasping manual movement they afford. The principal purpose of the present experiment was to determine if such visuomotor priming also concerns the reaching manual movement that visual objects afford. During a perceptual decision task, 32 subjects were asked to grasp a proximal or distal switch, as fast and accurately as possible, depending on the color of a chess piece displayed on a computer screen. Results showed an effect on the reaction times of the interaction between the position of the chess piece on the chessboard and the manual response, suggesting that subjects mentally simulated a manual reaching movement toward the perceived chess piece.

Adult↗
PubMed2003

Visual masking as a probe for abnormal gamma range activity in schizophrenia.

BACKGROUND: Visual masking procedures assess very early stages of visual perception. Patients with schizophrenia consistently show deficits on visual masking tasks, and these deficits likely reflect vulnerability to schizophrenia. We conducted two experiments to determine whether visual masking procedures can reveal underlying abnormalities in gamma range oscillations in schizophrenia. METHODS: In the first experiment, we conducted nonlinear modeling of visual masking performance data from 89 male schizophrenic patients and 20 male comparison subjects. In the second experiment, electrophysiological recordings of event-related gamma activity were taken during a visual masking task in a subset of eight patients and seven control subjects. RESULTS: In the first experiment, nonlinear modeling of the performance data revealed evidence of oscillations in the gamma range (30 and 35 Hz) for the comparison group but not patients. In the second experiment, the comparison group, but not the patients, showed a burst of gamma range activity 200-400 msec following target presentation. The difference between patients and comparison subjects in this time period was significant (p <.05). CONCLUSIONS: Visual masking procedures can serve as a probe for underlying gamma range activity, which appears to be aberrant in schizophrenia. Perceptual problems in schizophrenia may, at least in part, be due to a failure to establish and/or maintain gamma range oscillations.

Case-Control Studies↗
PubMed2006

Activation of color-selective areas of the visual cortex in a blind synesthete.

Many areas of the visual cortex are activated when blind people are stimulated naturally through other sensory modalities (e.g., haptically; Sadato et al., 1996). While this extraneous activation of visual areas via other senses in normal blind people might have functional value (Kauffman et al., 2002; Lessard et al., 1998), it does not lead to conscious visual experiences. On the other hand, electrical stimulation of the primary visual cortex in the blind does produce illusory visual phosphenes (Brindley and Lewin, 1968). Here we provide the first evidence that high-level visual areas not only retain their specificity for particular visual characteristics in people who have been blind for long periods, but that activation of these areas can lead to visual sensations. We used fMRI to demonstrate activity in visual cortical areas specifically related to illusory colored and spatially located visual percepts in a synesthetic man who has been completely blind for 10 years. No such differential activations were seen in late-blind or sighted non-synesthetic controls; neither were these areas activated during color-imagery in the late-blind synesthete, implying that this subject's synesthesia is truly a perceptual experience.

Association↗
PubMed1998

Effects of an ELF (50 Hz, 1 mT) electromagnetic field (EMF) on concentration in visual attention, perception and memory including effects of EMF sensitivity.

To investigate psychological effects of an extremely low frequency (ELF)-electromagnetic field (EMF), an experiment with three conditions was designed. EMF field of 50 Hz and 1 mT accompanied by 45 dB SPL noise (EMF + noise), noise, and control. A group of 66 subjects (Ss) participated in the control and in one of the experimental conditions. The sequence of conditions (expositions) was balanced. Expositions were double-blind (except for the obvious control), lasted 1 h and were separated by a 1 h pause. During exposition Ss (three by three) performed tests on attention, perception, memory and filled out a psychological questionnaire. Statistical analysis (one-tailed probability) showed less attention (P < 0.05), perception (P < 0.05) and memory performance (P < 0.1) in Ss exposed to EMF + noise compared with control, whereas for noise versus control no difference was found. Comparing EMF + noise versus noise related to control, reduced perception, less memory performance and more discomfort was observed (P < 0.1). Dividing Ss according to their self-rated sensitivity to EMF, all differences disappeared in the low sensitivity group (N = 30) and were pronounced in sensitive Ss (N = 36). Results indicate an immediate reduction of cognitive performance in attention, perception and memory performance by a 50 Hz EMF of 1 mT. These effects seem to be modulated by the self-perception of sensitivity to EMF.

Adult↗
PubMed2000

Distributed neural systems for the generation of visual images.

Visual perception of houses, faces, and chairs evoke differential responses in ventral temporal cortex. Using fMRI, we compared activations evoked by perception and imagery of these object categories. We found content-related activation during imagery in extrastriate cortex, but this activity was restricted to small subsets of the regions that showed category-related activation during perception. Within ventral temporal cortex, activation during imagery evoked stronger responses on the left whereas perception evoked stronger responses on the right. Additionally, visual imagery evoked activity in parietal and frontal cortex, but this activity was not content related. These results suggest that content-related activation during imagery in visual extrastriate cortex may be implemented by "top-down" mechanisms in parietal and frontal cortex that mediate the retrieval of face and object representations from long-term memory and their maintenance through visual imagery.

Adult↗
PubMed2004

The neural fate of consciously perceived and missed events in the attentional blink.

Cognitive models of attention propose that visual perception is a product of two stages of visual processing: early operations permit rapid initial categorization of the visual world, while later attention-demanding capacity-limited stages are necessary for the conscious report of the stimuli. Here we used the attentional blink paradigm and fMRI to neurally distinguish these two stages of vision. Subjects detected a face target and a scene target presented rapidly among distractors at fixation. Although the second, scene target frequently went undetected by the subjects, it nonetheless activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). This PPA activation was amplified when the stimulus was consciously perceived. By contrast, the frontal cortex was activated only when scenes were successfully reported. These results suggest that medial temporal cortex permits rapid categorization of the visual input, while the frontal cortex is part of a capacity-limited attentional bottleneck to conscious report.

Analysis of Variance↗