Architecture of Cortex Revealed by Divided Attention Experiments

Divided attention is investigated in concurrent tasks of letter recognition and second-order motion detection. I developed a quantitative method, Structure-Attention Mapping (SAM), to explain my data and to relate concurrent psychophysical experiments to the architecture of human visual cortex. A dual task paradigm, in which the interference between two tasks indicated the nature of processing involved was used. Subjects performed concurrent tasks of letter recognition and motion detection of second-order motion stimuli under diierent attentional instructions. Based on the task performances, the subjects fell into two very distinct groups. This suggested that both second-order and third-order motion processes were activated, but to signiicantly diierent degrees in the two groups. Third-order motion detection interfered with letter-recognition, while second-order motion detection did not. Additional experiments showed that two concurrent second-order motion tasks interfered with each other as did two third-order motion tasks. The diierence in interference patterns of the two motion processes suggests that second-order motion may be computed entirely in the dorsal stream (spatial processing) while third-order motion consists of two computational processes , one of which occurs in the ventral stream (pattern recognition), and shares computational resources with the letter-recognition task.