Hemispheric asymmetries for an inspection time task: a general left hemisphere temporal advantage?

Two thematic versions of an inspection time task were administered to 18 normal, right-handed subjects. For both tasks, subjects were required to make a categorical discrimination related to the length of two lines. In one version of the task (time task), difficulty was manipulated by varying the exposure duration of the lines. In the other version (length task), difficulty was manipulated by varying the degree to which one line was shorter than the other. The time task was designed to measure the temporal acuity of the observer while the length task was used to gauge subjects' capacity for the same categorical discrimination; independent of temporal acuity. Thus, the two tasks were designed to dissociate the categorical and temporal aspects of the inspection time task. Divided visual field techniques revealed a significant left hemisphere (LH) advantage for the time task, but no asymmetry for the length task. These results could not be accounted for in terms of the categorical nature of the representation. A model, related to the LH's predisposition for the detection of fine temporal events provided a more satisfactory account of the results.