THE EFFECTS OF ECCENTRICITY AND STIMULUS MAGNIFICATION ON SIMULTANEOUS PERFORMANCE IN POSITION AND MOVEMENT ACUITY TASKS

We presented two tasks, spatial interval discrimination and displaceme nt detection, simultaneously in the same location at various eccentric ities. The subject was to solve (i) only the spatial interval task; (i i) only the displacement task; or (iii) both tasks simultaneously. Wit h 500 msec stimulus duration, and using the method of spatial scaling, the E-2 value (the eccentricity at which stimulus size has to be doub led to maintain performance level) was found to be 0.17-0.39 deg for s patial interval discrimination and 1.0-1.2 deg for displacement detect ion. These values remained unaffected whether the subject solved one t ask or two tasks simultaneously. This finding was confirmed using a sh orter, 50 msec stimulus duration. As there is no interference between tasks, the mechanisms solving the tasks appear to be functionally inde pendent i.e., operating in parallel at all eccentricities. (C) 1997 El sevier Science Ltd.