An experiment was conducted to examine the influence of luminance, contrast, and spatial frequency content on saccadic eye movements. 112 pictures of natural textures from Brodatz were low-pass filtered (0.04 – 0.76 cycles deg−1) and high-pass filtered (1.91 – 19.56 cycles deg−1) and varied in luminance (low and high) and contrast (low and high), resulting in eight images per texture. Circular clippings of the central parts of the images (approximately 15% of the whole image) were used as stimuli. In the condition of bottom - up processing, the eight stimuli derived from one texture were presented for 1500 ms in a circular arrangement around the fixation cross. They were followed by a briefly presented target stimulus in the centre, which in half the trials was identical to one of the eight test stimuli. Participants had to decide whether the target stimulus was identical to any of the preceding stimuli. During a trial, their eye movements were recorded by means of a Dual-Purkinje-Image eye tracker. In the top - down condition, the target stimulus was presented in each trial prior to the display of the test stimulus. It was assumed that the priming with a target produced a top - down processing of the test stimuli. The latency and landing site of the first saccade were computed and compared between the top - down and bottom - up conditions. It is hypothesised that stimulus characteristics (luminance, contrast, and spatial frequency) play a more prominent role in bottom - up processing, while top - down processing is adjusted to the particular characteristics of the prime.
Supplemental Material for Failures in Top-Down Control in Schizophrenia Revealed by Patterns of Saccadic Eye Movements
