Vernier and contrast discrimination in central and peripheral vision

The present paper asks whether Vernier offset discrimination is limited by the observer's sensitivity to local contrast change in both central and per ipheral vision. To answer this question we compared Vernier discrimination and contrast discrimination thresholds (specified in the same units) for a pair of narrow ribbons of cosine gratings. Because the ribbons are narrow, both the offset information (for Vernier discrimination) and the contrast i nformation (for contrast discrimination) are highly localized. We found tha t when the stimuli are narrow ribbons, the local contrast cue is the limiti ng factor in Vernier discrimination. However, our results also show that in tegration of information along the length of the gratings (the ribbon width ) is: (i) different for Vernier and contrast discrimination, and (ii) for V ernier discrimination the integration of information along the length of th e gratings differs qualitatively in central and peripheral vision. For narr ow ribbons, the peripheral 'template' for ribbon Vernier acuity is not as w ell matched to the stimulus (in two-dimensional spatial frequency space) as the foveal 'template'. (C) 2000 Elsevier Science Ltd. All rights reserved.