Long Range Lateral Interaction in the on and off Visual Pathways of Humans

The human periphery effect (PE) is characterized by changes in target thresholds when the luminance of retinal areas that are located remote from the target locus is modulated. This study sought to determine whether the PE occurred in the ON and OFF visual pathways in humans, whether the magnitude of the PE was similar in the two pathways, and whether the observed effects were retinal or cortical in origin. This was done by determining the effect of peripheral stimulation on thresholds for detecting of flicker in rapid ON and rapid OFF sawtooth temporal waveforms. Five subjects set thresholds, in four different paradigms, for detection of flicker in rapid ON and rapid OFF luminance modulated foveal stimuli. Stimuli were 1.2 deg and presented on a 4 deg steady white background of 41.0 cd/sq m. Surrounding the background was a luminance-matched 16.0 deg x 22.0 deg field that was either unmodulated (uniform control) or a 0.25-cpd vertical square wave grating that was counterphase modulated at 7.5 Hz. In Experiment 1, the test stimuli were flickered rapid ON or rapid OFF sawtooth waveforms on top of the background, whereas, in Experiment 2, they were modulated around the mean luminance of the background. In Experiment 3, the surrounding grating and target were either presented to the same or opposite eyes in a dichoptic viewing situation. Finally, in Experiment 4, full field flicker in the periphery was used to investigate the underlying neural organization of the lateral interactions in the ON and OFF pathways.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'Long Range Lateral Interaction in the on and off Visual Pathways of Humans', published 2004 under ISBN 9781423519027 and ISBN 1423519027.