Visual Attention Effects on Discrimination of Line Orientation and Line Arrangement.

Abstract : The distinction between visual processes that require focused attention and those that use more diffuse or global attention is largely based on studies of visual search and texture segregation. It has been inferred from these studies that stimuli differing in the orientation of their component line segments can be distinguished without focal attention, whereas stimuli that differ only in the arrangement discrimination. In the first of the present experiments, while maintaining central fixation, attention was directed to a relevant peripheral target by a cue presented in the appropriate location. Discrimination of targets that differed in orientation of lines was minimally facilitated as the time between the onset of the valid cue and the onset of the target was increased from 17 msec to 268 msec. On the other hand, discrimination of targets composed of two conjoining line segments (sideways Ts) required time to shift and focus attention, and benefits increased with longer cue-target SOAs that allowed attention to accumulate at the target. To test whether orientation discrimination would be affected by focusing attention elsewhere in the visual field, a second experiment was conducted in which a cue misdirected attention on 20% of the trials. A decrement occurred on incorrectly cued trials in comparison to correctly cued trials for both types of stimuli, SLANTs and Ts.