The effects of coarseness of quantisation, exposure duration, and selective spatial attention on the perception of spatially quantised ('blocked') visual images.

The two objectives of the present article are (a) to present a brief overview of the effects of systematic variation of the spatial-scale value of quantisation and stimulus duration on the identification of original images that have been degraded by Harmon-Julesz type of image pixelisation by 'blocking' and (b) to report the results of two experiments where the effects of selective spatial precuing by local and global peripheral precues on the identification of quantised target stimuli have been studied. Both the overview and the new results reported here demonstrate some counter-intuitive effects: (1) abrupt decrease in identification efficiency with only a minor change in the coarseness of quantisation over a critical value of pixels per stimulus; (2) a cost for valid attentional precuing with coarse-quantised images. If physical precues (exposed with stimulus onset asynchrony of 120 ms) were employed in order to orient spatial attention to perceive original or fine-quantised stimuli, then attentional facilitation was found. However, if the precued stimuli were coarse quantised then the facilitative effect crossed over to a detrimental effect of attention. These effects are discussed in the context of the microgenetic approach that presupposes the existence of a perceptual-attentional processing routine that operates according to the coarse-to-fine time-course rule of selective attentional activation of stimulus representations at various spatial scales.