Raised visual detection thresholds depend on the level of complexity of cognitive foveal loading

The objective of the study was to measure the interactions between visual t hresholds for a simple light (the secondary task) presented peripherally an d a simultaneously performed cognitive task (the primary task) presented fo veally. The primary task was highly visible but varied according to its cognitive c omplexity. Interactions between the tasks were determined by measuring dete ction thresholds for the peripheral task and accuracy of performance of the foveal task. Effects were measured for 5, 10, 20, and 30 deg eccentricity of the peripherally presented light and for three levels of cognitive compl exity. Mesopic conditions (0.5 lx) were used. As expected, the concurrent presentation of the foveal cognitive task reduc ed peripheral sensitivity. Moreover, performance of the foveal task was adv ersely affected when conducting the peripheral task. Performance on both ta sks was reduced as the level of complexity of the cognitive task increased. There were qualitative differences in task interactions between the centra l 10 deg and at greater eccentricities. Within 10 deg there was a dispropor tionate effect of eccentricity, previously interpreted as the 'tunnel-visio n' model of visual field narrowing. Interactions outside 10 deg were less a ffected by eccentricity. These results are discussed in terms of the known neurophysiological characteristics of the primary visual pathway.