Reduced Interocular Transfer of Spatial Adaptation for Fast Stimuli

Threshold elevation following monocular adaptation is weaker in the unadapted eye than in the adapted eye. At least 15 studies have measured this interocular transfer (IOT) phenomenon, and typically report around 60% transfer. Yet almost all of these studies used spatial frequencies above 3c/deg, very slow temporal parameters, and criterion sensitive methods (method of adjustment, yes/no). In recent work, we (Meese and Baker 2011, i-Perception 2 159–182) found markedly weaker interocular transfer at low spatial and high temporal frequencies. Here, we measure IOT in 9 observers for a broad range of spatiotemporal frequencies (0.5, 2, and 8c/deg; 1, 4, and 15Hz) using a 2AFC paradigm. Targets were horizontal Gabor patches with a full-width-at-half height of 1.67 (lower frequencies) or 6.68 (8c/deg) grating cycles. Adaptors were larger gratings with the same spatiotemporal properties as the targets. Observers adapted for 2 min initially, and 5 s between each trial, with monocular presentation enabled by shutter goggles. We typically found weaker IOT than previously reported (<50%), particularly for our fastest stimuli (lowest spatial and highest temporal frequencies), where it was virtually absent in all cases. Binocular summation and monocular adaptation were normal in all conditions. This implies that adaptation to ‘magno’ stimuli, not investigated in previous studies, occurs at a monocular locus. We also consider possible methodological confounds in classical studies which might have inflated the levels of IOT. These include the formation of retinal afterimages from static adaptors and changes in criterion unrelated to changes in sensitivity