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 detectability of tactile stimuli, but the effects on a more complex perceptual task, the discrimination of surface texture, are unknown. This study sought to examine whether attention influences the ability to discriminate a change in texture during passive touch. Twelve subjects were trained to perform two discrimination tasks: discriminating an increase in the intensity of a visual stimulus, and discriminating a change in the texture of a surface that was displaced beneath the tip of one digit. The texture change consisted of an increase in the spatial period between rectangular arrays of raised dots on Nyloprint surfaces, and for each subject an increment close to his or her discrimination threshold was employed in the experiment. Each trial began with the presentation of two baseline stimuli: A standard voltage illuminated the visual stimulus (an array of yellow light-emitting diodes (LEDs), and a standard texture (3-mm spatial period) was displaced under the tip of digit 3. For visual trials, three different increments in luminous intensity were presented, at one of three different delays following the initial presentation of the baseline stimuli. For texture trials, a single increment in spatial period was presented at one of three delays after the onset of the baseline stimuli. In any one trial, only one modality changed in intensity. The subject's task was to signal, as quickly 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 might change, or to direct the subjects' attention toward the modality that did not change (invalid cue). Two measures of performance were employed: accuracy (percentage correct) and reaction time (speed with which the subject responded). The results indicated that cue condition significantly influenced the ability of subjects to discriminate a change in texture: Both accuracy and speed were significantly improved when subjects' attention was selectively directed toward the textured surface, as compared to when it was misdirected toward the visual modality. Performance was intermediate when attention was divided between the two 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 significantly influenced both tactile detection and tactile discrimination; however, the relative effects on response latencies were not constant across these tasks, the effects being greater for tactile detection than for tactile discrimination.