The Cost of Spatial-Attentional Precuing for the Perception of Spatially Quantised Visual Images

We have investigated the effects of selective attentional spatial precuing and levels of quantisation on the perception of spatially quantised visual images of faces. The coarseness (number of square-shaped isoluminant pixels per image) of quantisation of eight alternative facial images was systematically varied from 9 to 16 pixels per image (along the horizontal dimension). 16 grey levels of the image were used; both local and global precues that designated the position of the expected stimulus-image were employed. Precue-to-target stimulus onset asynchrony was equal to 120 ms, and target image duration was varied between 28 and 76 ms. Targets were exposed at one of four quasiperipheral positions, either after the precue or without the precue. It was found that precues had a facilitative effect on identification with fine levels of quantisation or with original images, but this changed to a cost for precuing with coarse levels (9 – 11 pixels per image). A dramatic drop in overall identification efficiency with moving from 12 pixels per image to 11 pixels per image condition was also revealed. The results are interpreted as supporting (1) the idea of gradual coarse-to-detailed presetting of spatial filters by the precue, and (2) the existence of some implicit relational metrics of the critical facial identity cues that can be ‘catastrophically’ disintegrated by a small but critical change in quantisation value.