Biomedical subjects

Leila Montaser-Kouhsari

Publications and source records attributed to Leila Montaser-Kouhsari.

4 recordsLinked to original sources

PubMed2004

Subliminal attentional modulation in crowding condition.

In the crowding phenomenon, recognition of a visual target is impaired by other similar visual stimuli (distracters) presented near the target. This effect may be due largely to insufficient resolution of spatial attention. We showed that attention could subliminally enhance orientation selective adaptation to illusory lines in the crowding condition where target-distractor separation is beyond the limit of spatial resolution of attention. Despite the traditionally held close link between attention and awareness, here we provided evidence for subliminal attentional modulation for orientation stimuli that could not have been consciously perceived.

Adult↗

PubMed2004

Attentional modulation of adaptation to illusory lines.

Selective visual attention modulates neuronal activation in various cortical areas. This type of neuronal modulation could happen even in the early stages of visual processing where specific attributes of visual stimuli are processed. It has been shown that different forms of visual aftereffects, such as tilt aftereffect, motion aftereffect, and figural aftereffect, are modulated by attention. In this study, we investigated the effect of visual attention on adaptation to illusory lines. In the first experiment, orientation selective adaptation to a peripheral illusory line was measured in three conditions: (1) poor attention condition in which subjects performed a dual task (even-odd judgment) at the fixation point during the adaptation period, (2) partial attention condition in which subjects only observed successively presented digits at the fixation point and did not perform the task during the adaptation period, and (3) full attention condition in which no visual stimuli were presented at the fixation point. Results showed that the magnitude of adaptation systematically decreased as the attentional load at the fixation point increased. In the second experiment, two transparent illusory contours were presented during the adaptation period, and tilt aftereffects to attended and non-attended illusory lines were compared. The magnitude of tilt aftereffect to the attended illusory line was significantly greater than that to the non-attended illusory line even when non-attended illusory contour was more visually salient. Because visual areas V2 and V1 are the first stage in the processing of illusory contours, we could conclude that visual attention has modulatory effects on the activation of neurons in these areas.

Adaptation, Ocular↗

PubMed2004

Orientation-selective adaptation during motion-induced blindness.

When a global moving pattern is superimposed on high-contrast stationary or slowly moving stimuli, the latter occasionally disappear for periods of several seconds (motion-induced blindness, MIB). Here, an adaptation paradigm was used to determine if orientation-selective adaptation still occurs for the stimulus that is no longer visible. Two slowly drifting high-contrast Gabor patches were presented to observers. As soon as both patches disappeared, one was eliminated from the screen. After 2 s, two low-contrast Gabor patches were presented as tests at the same locations and observers were asked to report their orientations. The observers' performance was significantly higher when the orientation of the low-contrast test patch was orthogonal to the orientation of the high-contrast adapting patch (p < 0.0001) for the location where the patch was present during MIB, even though it was perceptually invisible. The observers' performance was not significantly different at the adjacent control location where the stimulus was absent during the MIB. Although no stimulus was visible at either location, orientation-selective adaptation was preserved only for the location at which the patch remained present. Since orientation information is processed in low-level visual areas such as the primary visual cortex (V1), we conclude that MIB originates in an area higher than V1.

Adaptation, Psychological↗

PubMed2003

Orientation-selective adaptation to crowded illusory lines.

Visual adaptation has been successfully used as a psychophysical tool for studying the functional organisation of visual awareness. It has been shown that orientation-selective adaptation to a grating pattern occurs in crowded conditions. In such conditions, simultaneous presentation of flanking distractors pushes the target stimulus out of conscious perception and severely impairs orientation discrimination in the periphery of the visual field. In the present study, orientation-selective adaptation to illusory lines induced by two line gratings abutting each other with a phase shift was examined in crowded and non-crowded conditions. To rule out the effects of lower level adaptations we used an animation paradigm in which the orientations of the two line gratings were altered repeatedly during adaptation phase without any change in the orientation of the resulting illusory line. Although performance of subjects in reporting the orientation of crowded illusory lines was at chance level, orientation-selective adaptation was preserved for crowded as well as non-crowded adapting targets. Two control experiments demonstrated that adaptation to endpoints of real lines at the location of abutting grating lines had minimal effect on the adaptation to illusory lines; and changes in the configuration of endpoints could not be responsible for better performance when adapting and test stimuli were different. We conclude that a crowding effect occurs after illusory lines have been processed in the visual stream. Since illusory lines seem to be represented at relatively early stages of visual processing (e.g. area V2), adaptation to crowded illusory stimuli suggests that neuronal activation in those early stages is not necessarily correlated with conscious perception.

Adaptation, Ocular↗