Examining the differential aging of the ambient and focal visual systems: An approach using the peripheral detection task during simulated driving

The purpose of this project was to investigate the recently popular peripheral detection task (PDT) in an attempt to further understand the true nature of its diagnosticity. Rather than measuring attention in the traditional sense, an alternative approach was used which explains information processing in terms of two unique, yet non-exclusive visual systems; referred to as the "ambient and focal systems." The focal system is used for object identification while the ambient system is responsible for object localization and visuomotor functions. Ambient system abilities were operationalized by temporally modulating the signal strength of peripherally located LED targets in an attempt to test the recently suggested ambient insufficiency hypothesis for explaining age-related changes in visual system sensitivity. Sixteen young (M=23 years) and eighteen older (M=72 years) subjects were required to operate a simplistic driving simulator during conditions of varying workload and target location predictability while receiving targets of differing ambient ability (low, moderate, or high). Older subjects exhibited significantly lower PDT hit rates as a function of increasing simulator workload demands and decreasing target location predictability. However, the failure to observe any additional age-specific interactions with the ambience manipulation suggests that all subjects, regardless of age, were relying on top-down periodic scanning of the target area using focal vision to detect peripheral targets. These results bring into question the validity of the ambient insufficiency hypothesis. On the contrary, after reassigning the older group of subjects to performance-based groups, post hoc analyses revealed that those with poorer overall detection rates exhibited a decline in sensitivity for targets theoretically designed to maximally stimulate ambient system processing. In addition, those older subjects with better overall detection rates remained indistinguishable from those of the younger group. This suggests that a select group of senescent individuals in the current sample were no longer able to reliably capitalize on targets specifically designed to trigger preemptive, ambient processing. Such findings indicate a change in ambient system sensitivity for some, but perhaps not all aging persons; thereby providing preliminary support for the ambient insufficiency hypothesis.