Fig. 1.

Effect of binaral concentration disparity on heading perception based on optic flow. (A) Schematic illustration of an exemplar trial in the heading-judgment task. Heading angle α was defined as the angle between straight ahead and the center of expansion of an optic-flow stimulus and varied from trial to trial in random order. ITI, intertrial interval; Resp: L/R?, response: left or right?. (B) Participants performed the heading-judgment task while smelling one concentration of a nontrigeminal odorant in a nostril and a second concentration in the other nostril. (C–E) Percentages of rightward responses plotted as a function of the physical heading angle α of the optic-flow stimuli, when the 3 groups of participants in Experiment 1 smelled a higher concentration of phenylethyl alcohol (PEA) in the left nostril (L > R) and in the right nostril (L < R), respectively fitted with sigmoidal curves. Insets illustrate the corresponding PSE shifts induced by high (C), intermediate (D), and low (E) binaral disparities relative to zero disparity. The average percentages of rightward responses at α = −2 and 2° were less than 1% and over 99%, respectively, and are not displayed. Error bars indicate SEMs adjusted for individual differences. **P < 0.01. conc., concentration.