EFFECTS OF CROSS-MODAL MANIPULATIONS OF ATTENTION ON THE ABILITY OF HUMAN-SUBJECTS TO DISCRIMINATE CHANGES IN TEXTURE

Cross-modal manipulations of attention significantly affect the detect ability of tactile stimuli, but the effects on a more complex perceptu al task, the discrimination of surface texture, are unknown. This stud y sought to examine whether attention influences the ability to discri minate a change in texture during passive touch. Twelve subjects were trained to perform two discrimination tasks: discriminating an increas e in the intensity of a visual stimulus, and discriminating a change i n the texture of a surface that was displaced beneath the tip of one d igit. The texture change consisted of an increase in the spatial perio d between rectangular arrays of raised dots on Nyloprint surfaces, and for each subject an increment close to his or her discrimination thre shold was employed in the experiment. Each trial began with the presen tation of two baseline stimuli: A standard voltage illuminated the vis ual stimulus (an array of yellow light-emitting diodes (LEDs), and a s tandard texture (3-mm spatial period) was displaced under the tip of d igit 3. For visual trials, three different increments in luminous inte nsity were presented, at one of three different delays following the i nitial presentation of the baseline stimuli. For texture trials, a sin gle increment in spatial period was presented at one of three delays a fter the onset of the baseline stimuli. In any one trial, only one mod ality changed in intensity. The subject's task was to signal, as quick ly as possible, the occurrence of the change. Instructional cues (red and green LEDs) were used to direct the subjects' attention toward the modality that changed (valid cue), to divide the subjects' attention between the visual and tactile modalities (neutral cue) as either migh t change, or to direct the subjects' attention toward the modality tha t did not change (invalid cue). Two measures of performance were emplo yed: accuracy (percentage correct) and reaction time (speed with which the subject responded). The results indicated that cue condition sign ificantly influenced the ability of subjects to discriminate a change in texture: Both accuracy and speed were significantly improved when s ubjects' attention was selectively directed toward the textured surfac e, as compared to when it was misdirected toward the visual modality. Performance was intermediate when attention was divided between the tw o modalities. The results were compared with those obtained previously in a tactile detection task using a similar attentional manipulation. It was concluded that this cross-modal manipulation of attention sign ificantly influenced both tactile detection and tactile discrimination ; however, the relative effects on response latencies were not constan t across these tasks, the effects being greater for tactile detection than for tactile discrimination.