Target detection in left and right hemispace

Traditionally, spatial processing has been considered the domain of the right hemisphere(e.g., Milner, 1974; Sperry, 1974). Recent research however, suggests that both hemispheres may play a role in analyzing spatial information with each contributing in a different manner (e.g., Robertson & Lamb, 1991). Five experiments presented here explore hemispheric differences in one particular aspect of spatial processing, namely the detection of a particular object or target that appears along with other items. In Experiment 1, subjects were asked to detect a target digit within an array of six digits when either all of the items in the array other than the target were the same (Homogeneous condition) or when they were all different (Heterogeneous condition). Results suggested that the right hemisphere is more sensitive to the background in which the target appeared. In Experiment 2, subjects were asked to detect a target in an array in which the location of the background digits varied from trial to trial. The results suggested that positional uncertainty in the array aided the right hemisphere while hindering the left. In Experiment 3, the results of Experiment 1 were confirmed in a forced-choice paradigm. Experiment 4 examined the effect presenting two targets in the array. Results demonstrated that when two targets were presented in an array, each hemisphere continued to process the information it received independent of the processing of the other hemisphere. In Experiment 5, subjects viewed arrays composed of chevron figures. This experiment added a condition in which the distractor figures themselves composed the elements of a larger figure or Gestalt. It was hypothesized that the results for the Homogeneous and Heterogeneous backgrounds would be the same as in previous experiments and that the Gestalt condition would have a greater effect on right hemisphere processing. Results of the five experiments are discussed in light of proposed model of hemispheric control of attention.U of I OnlyETDs are only available to UIUC Users without author permissio