SPATIAL-FREQUENCY AND CONTRAST TUNING OF THE TRANSIENT-STEREOPSIS SYSTEM

The tuning of the transient-stereopsis system to luminance contrast an d spatial-frequency (SF) was investigated with narrow-band gabor targe ts with a constant sigma of 1 degrees. They were presented for brief ( 140 ms) durations and subtended a large (6 degrees) disparity. When di choptic gabor stimuli were matched in SF (0-5 cpd), transient stereo p erformance was either uniform across SF or greater at frequencies belo w 1 cpd. When dichoptic stimuli had unmatched SF (0.5 + 0-5 cpd) and m atched contrast (100%), stereo performance was impaired below that of the matched SF condition. Stereo performance with matched SF at 0.5 cp d was impaired when contrast of one eye's image was reduced, demonstra ting a contrast-paradox effect (i.e. contrast tuning) for transient st ereopsis. Performance with three dichoptic unmatched SF conditions (0. 5 and 1.0 cpd; 0.5 and 5.0 cpd; 1.5 and 3.5 cpd)was improved when the contrasts of the low SF gabor was reduced while holding the contrast o f the high SF gabor constant at 100%. However stereo performance was n ot improved by reducing the contrast of a high SF gabor (3.5 cpd) whil e holding the contrast of the lower SF gabor (1.5 cpd) constant at 100 %. We interpret these findings as indicating that transient-stereopsis performance is mediated by a single spatial-channel that has low-pass spatial-frequency sensitivity and which compares the ocular based sig nals prior to binocular combination so that signals that are not balan ced in terms of their strength lead to a weaker binocular signal, as p er the model proposed by Kontsevich and Tyler (Vis Res 1994;3417:2317- 2329) for sustained stereopsis. (C) 1998 Elsevier Science Ltd. All rig hts reserved.