Asynchronous stimulus presentation in visual extinction: A psychophysical study

Patients showing visual extinction as a consequence of a unilateral brain lesion can correctly detect a single stimulus in either hemifield but fail to detect the contralesional stimulus (or at least process the stimulus less efficiently) when it is presented simultaneously with an ipsilesional stimulus. In an attempt to uncover the nature of the underlying deficit, some studies have manipulated the temporal characteristics of stimulus presentation. Contra- and ipsilesional stimuli with different stimulus onset asynchronies are typically used. In the present study, visual extinction was investigated in a group of left neglect patients (N=10) using a psychophysical paradigm with different stimulus onset asynchronies of target and distractor stimuli presented in different hemifields. Contrast thresholds for a target grating were determined with the target either in isolation or in the presence of an irrelevant distractor grating. When target and distractor gratings were presented simultaneously, neglect patients showed a significant extinction effect, i.e., a significant interference from the right hemifield distractor with left hemifield contrast sensitivity. When the right hemifield distractor preceded the left hemifield target stimulus by 250 ms, two different patterns of results were observed in the neglect patients. Five patients showed a significant improvement compared to the simultaneous presentation condition, five other patients showed a significant increase of the extinction effect. The results suggest that different underlying mechanisms, maybe due to different lesion locations, can cause extinction in neglect patients.     

Malvine Husserls “Skizze eines Lebensbildes von E. Husserl”

Ohne Zusammenfassung     

Locational uncertainty moderates affective congruency effects in the evaluative decision task

Affective congruency effects are often investigated using the evaluative decision task. It was predicted that uncertainty about the location of stimulus presentation moderates the strength of affective congruency effects in this task. In line with this hypothesis, effects of affective congruency were observed in two experiments only if locational uncertainty about the target location required participants to distribute their attention evenly over the visual field. Inducing certainty about the target location allowed participants to narrow their attentional focus and to suppress the influence of irrelevant distractor words. The results suggest that affective congruency effects in the evaluative decision task are not exclusively based on automatic processes, but also depend on a strategic and flexible allocation of attention.