Contrasting the edge- and surface-based theories of object recognition: behavioral evidence from macaques (Macaca mulatta)

Abstract

This study assessed the contribution of edge and surface cues on object representation in macaques (Macaca mulatta). In Experiments 1 and 2, 5 macaques were trained to discriminate 4 simple volumetric objects (geons) and were subsequently tested for their ability to recognize line drawings, silhouettes, and light changes of these geons. Performance was above chance in all test conditions and was similarly high for the line drawings and silhouettes of geons, suggesting the use of the outline shape to recognize the original objects. In addition, transfer for the geons seen under new lighting was greater than for the other stimuli, stressing the importance of the shading information. Experiment 3, using geons filled with new textures, showed that a radical change in the surface cues does not prevent object recognition. It is concluded that these findings support a surface-based theory of object recognition in macaques, although it does not exclude the contribution of edge cues, especially when surface details are not available.

Figure 1

Experiment 1: Representation of the four training edged geons A: a truss, B: a brick, C: a wedge, D: a prism. Some examples of the test stimuli: A′: line drawing of the truss; A″: silhouette of the truss; A‴, B‴, C‴, D‴: the original edged geons seen under a change in the light direction. Experiment 2: Representation of the four training smoothed geons A: a pear, B: a barrel, C: a noodle, D: a cone. Some examples of the test stimuli: A′: line drawing of the pear; A″: silhouette of the pear; A‴, B‴, C‴, D‴: the original smoothed geons seen under a change in the light direction. Experiment 3: Representation of the four training geons. A: an arch (smoothed geon), B: a diabolo (smoothed geon), C and D: two different prisms (edged geons). Some examples of the test stimuli: A′: the arch rendered with a pattern of dots, A″: the arch rendered with a pattern of parallel lines, C′: the prism rendered with a pattern of dots, C″: the prism rendered with a pattern of parallel lines.

Figure 2

Mean percentage of correct responses (with standard error bars) for each stimulus type for the test phase of Experiment 1.

Figure 3

(A) Mean percentage of correct responses (with standard error bars) for the first and the second test trials of Experiment 1, averaged for the five monkeys, the 12 test stimuli, and the 15 test sessions. (B) Mean percentage of correct responses (with standard error bars) across the 15 test trials of Experiment 1, averaged for the two test trials, the 12 test stimuli, and the five monkeys.

Figure 4

Mean percentage of correct responses (with standard error bars) for each stimulus type for the test phase of Experiment 2.

Figure 5

(A) Mean percentage of correct responses (with standard error bars) for the first and the second test trials, averaged for the five monkeys, the 12 test stimuli, and the 15 test sessions of Experiment 2. (B) Mean percentage of correct responses (with standard error bars) across the 15 test trials of Experiment 2, averaged for the two test trials, the 12 test stimuli, and the five monkeys.

Figure 6

Mean percentage of correct responses (with standard error bars) for each stimulus type for the test phase of Experiment 3.