Fig. 4: Circularity judgment task and example psychometric curves.
a, b Example pairs of Gabor stimuli (a) and their true spatial extents (b) under the radial (orange box) and tangential (blue box) orientation conditions. Each pair consisted of standard and probe Gabors, which always had the same radial or tangential orientation but differed in aspect ratio (AR, \({\sigma }_{{{{{{\rm{radial}}}}}}-{{{{{\rm{axis}}}}}}}/{\sigma }_{{{{{{\rm{tangential}}}}}}-{{{{{\rm{axis}}}}}}}\)). The aspect ratio was fixed at 1 for the standard (lower left corners) and varied for the probe (upper-right corners). In each trial, observers briefly viewed the stimuli and selected the one appearing close to a perfect circle. c Example psychometric curves from a representative observer under the radial (orange) and tangential (blue) orientation conditions. The fraction of trials in which the standard stimulus was chosen is plotted as a function of the AR of the probe (\({{AR}}_{{{{{{\rm{probe}}}}}}}\)) in a given trial. In the radial orientation condition, the observer’s preference for the standard was lowest when the value of \({{AR}}_{{{{{{\rm{probe}}}}}}}\) fell around a certain value smaller than 1 (as indicated by the orange downward triangle, which marks an estimate of the minimum point of the psychometric curve). In the tangential orientation condition, such a minimum point was found at the value of \({{AR}}_{{{{{{\rm{probe}}}}}}}\) falling around a certain value slightly greater than 1 (as indicated by the blue downward triangle). By inverting these values of \({{AR}}_{{{{{{\rm{probe}}}}}}}\) at the minima of the psychometric curves, the perceived aspect ratios (ARpercs) were estimated. Dots, observed data; Solid lines, fitted psychometric functions; downward triangle, \({1/{AR}}_{{{{{{\rm{perc}}}}}}}\); Inset images on the x-axis, the probe Gabors at three \({AR}\) values (0.5, 1, 2). Orange and blue colors, the radial and tangential orientation conditions.
