Proximal and cognitively-induced accommodation.

The aim of this study was to investigate proximally-induced accommodation (PIA) at two levels of cognitive demand. PIA was assessed by comparing the open-loop accommodative responses to stimuli located at viewing distances of 6 m (0.17 D) and 0.33 m (3 D), respectively. The vergence and accommodation loops were opened by subjects monocularly viewing the targets through a 0.5 mm pin-hole. PIA was measured while subjects either were encouraged to relax and listened to popular music, or performed a relatively demanding mental arithmetic task (counting backwards in sevens). The results indicated that for 4 of the 12 subjects examined, increased cognitive demand produced a marked (greater than +/- 1.00 D) change in the magnitude of PIA. This finding suggests the presence of an interaction between the output of proximally- and cognitively-induced accommodation in these subjects. Such an interaction may hinder attempts to examine individual, non-optical components of accommodation.