Initial adaptation: 100s Top-up adaptation between trials: 8s

1. VSS Meeting - Monday (May 6) 2001 Shin’ya Nishida (1), Isamu Motoyoshi (1,2) and Shinsuke Shimojo (1,3) (1) NTT Communication Science Laboratories, Atsugi, Kanagawa, Japan (2) JSPS Research Fellow (3) Caltech, Pasadena, CA Test GAZE MODULATION OF VISUAL AFTEREFFECTS BACKGROUND • How does the visual system convert gaze-dependent (eye-centred) coordinate of visual space into gaze-independent (body/world/object-centred) coordinates? • Apparatus • In a dark room, the stimulus pattern was displayed on two monitors (SONY GDM F500R, 120Hz) controlled by a VSG2/3 system. • Procedures • [TAE, SAE, DTE] Measurement of the aftereffect strength by a double random staircase method with a 2AFC judgement • Gaze modulation of neuronal responses • The gain of neuronal response to visual stimuli is modulated by the direction of gaze. • First found in parietal areas (Andersen et al., 1985, 1990), but later found in other areas including V1 (Trotter & Celebrini, 1999 ). • The gain field generated by the gaze modulation is a candidate of neural basis for the coordinate conversion (Zipser et al., 1988; Pouget & Sejnowski, 1997). • Gaze modulation of visual aftereffects • Psychophysical correlate of the neural gaze modulation? • A gaze-contingent motion aftereffect had been demonstrated by Mayhew (1973 ). Gaze direction (Measurement order) • Initial adaptation: 100s • Top-up adaptation between trials: 8s • [TAE, SAE] Measurement of the nulling strength • [DTE] Threshold measurement by target localisation • [MAE] A 60s adaptation followed by the measurement of aftereffect duration • Subjects always kept their head direction straight ahead, hence rotated their eyes to gaze directly at a pattern. • Binocular viewing unless otherwise noted. • The adaptation pattern was presented on one side, and the test was presented pseudo-randomly on the same or opposite side. • The position of the test pattern was indicated by a tone presented at the end of adaptation, and by a dot grid pattern presented at the test location immediately before test presentation. Tilt aftereffect (Monocular) Tilt aftereffect Orientation LED -31.1ﾟ +31.1ﾟ 58 cm After adaptation to opposite directions of motion at different gaze directions, the motion aftereffect direction reverses as the observer changes the gaze direction. Left eye Right eye Size aftereffect Motion aftereffect QUESTIONS • Does the gaze direction actually modulate visual aftereffects? • How strong is the gaze modulation? • Does it generally occur for visual aftereffects, or only for specific types? • Does it occur even with monocular presentation? METHODS • Stimuli: A pair of Gabor patches presented on a grey rectangle background P=0.039 • Eye movement control 1: Regardless of the test position, the subjects had to make a two-step gaze shift from adaptation to test patterns via a marker on the midline. • Eye movement control 2: To match the retinal position of the image, the subjects Time P=0.090 Adaptation Gaze trajectory 1s Adaptation Test Detection threshold elevation Threshold contrast 4.7deg were required to align the dot grid pattern with the afterimage of the adapt pattern. • The gaze modulation of the threshold elevation did not reach statistical significance. • Large individual difference • The contrast threshold was higher at the adapted gaze direction, but control data measured with uniform filed adaptation also showed a similar tendency - The gaze modulation of the pattern adaptation might be apparently weakened by the gaze modulation of the light adaptation. CONCLUSIONS • The gaze direction can modulate visual aftereffects. • The modulation was modest (<20%). • The modulation occurs in a wide range of visual aftereffects examined so far (at least for some observers). • The gaze modulation is not due to binocular artifacts (because it occurs monocularly as well). Slow oscillation to avoid afterimage formation 1.27 cpd 0.9 cpd 60% 80% 2s 9.4deg Test 0.2s 1.8 cpd +/-15 deg 0.1s Tilt aftereffect (TAE) Size aftereffect (SAE) Summary results • RESULTS • Group data indicated that the tilt aftereffect, the size aftereffect and the motion aftereffect are modulated by the direction of gaze. • The aftereffect was significantly stronger when measured at the adapted gaze direction than when measured at the non-adapted gaze direction. • However, the modulation was small [(same-opposite)/same < 20%] and did not always appear in individual data. • Gaze modulation occurred with monocular viewing as well as with binocular viewing. • The gaze modulation cannot be ascribed to binocular artefacts such as changes in vergence angle, (horizontal and vertical) disparity and eye dominance. 30 cd/m2 3.37 cpd 2.36 deg/s Summary: Gaze modulation Motion aftereffect (MAE) Detection threshold elevation (DTE)