Visual Perception of Photographs of Rotated 3D Objects in Goldfish (Carassius auratus)

Abstract

This study examined goldfishes' ability to recognize photographs of rotated 3D objects. Six goldfish were presented with color photographs of a plastic model turtle and frog at 0° in a two-alternative forced-choice task. Fish were tested with stimuli at 0°, 90°, 180°, and 270° rotated in the picture plane and two depth planes. All six fish performed significantly above chance at all orientations in the three rotation planes tested. There was no significant difference in performance as a function of aspect angle, which supported viewpoint independence. However, fish were significantly faster at 180° than at +/-90°, so there is also evidence for viewpoint-dependent representations. These fish subjects performed worse overall in the current study with 2D color photographs (M = 88.0%) than they did in our previous study with 3D versions of the same turtle and frog stimuli (M = 92.6%), although they performed significantly better than goldfish in our two past studies presented with black and white 2D stimuli (M = 67.6% and 69.0%). The fish may have relied on color as a salient cue. This study was a first attempt at examining picture-object recognition in fish. More work is needed to determine the conditions under which fish succeed at object constancy tasks, as well as whether they are capable of perceiving photographs as representations of real-world objects.

Keywords: goldfish; object constancy; object discrimination; picture-object recognition; visual perception.

Figure 1

Schematic diagram of the experimental setup. (A) Test tank showing the position of the stimulus board and stimuli in the tank. (B) The stimulus board containing 0° stimuli (frog and turtle).

Figure 2

Photo of the experimental setup in the test tank showing a goldfish choosing the frog stimulus rotated 180° in the depth plane (rotated along the x-axis) by tapping on it.

Figure 3

Average testing trial time over stimuli orientations with 95% Tukey-adjusted confidence intervals.

Figure 4

Comparison of performance accuracy on stimuli orientation across our different studies. 95% confidence intervals from the fixed-effects meta-regression model are shown. The 2D black and white stimuli are from DeLong et al. [45], 3D color turtle and frog is from DeLong et al. [15], and 2D color photographs of turtle and frog is from the current study. The fish performed significantly worse at 0° and +/−90° on the current study compared to the 3D color turtle and frog study (there was no significant difference in performance at 180°). The fish performed significantly better on the current study compared to both studies with black and white stimuli.