The "barber-diamond" demonstrates the ability of depth-cues to influence our interpretation of moving features and hence of perceived direction of motion. To appreciate this illusion:

1. Wait until the image loads

2. View the resultant animation through a pair of red-green anaglyph glasses (green lens on right eye). Fixate on the gray target at the center of the stimulus.

3. Observe the depth ordering between the putative surfaces (two of the textured panels should appear in front of the grating while the remaining panels should appear to reside behind the grating).

4. Observe how the depth ordering configuration affects the perceived direction of grating motion. The leftward motion of the grating should elicit the perception of up-left and down-left motion depending on which depth ordering surrounds it.

*Note that these stimuli are not identical to those employed in our experiments. We employed stereo goggles with liquid crystal shutters (CrystalEyes PC, Stereographics Corporation; San Rafael, CA) to alternately transmit left- and right-eye views of the display monitor at a monocular frequency of 60 Hz. When closed, each lens attenuated all but 6% of the luminance from the image intended for the other eye. Moreover, all stimuli were rendered in shades of gray. Unlike our stimulus, the luminance of the bright bars of the barber-diamond grating for this anaglyph demo does not match the luminance of the textured bars in the textured barber-diamond.

Textured barber-diamonds
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To confirm that neuronal responses to barber diamonds were based on the ability of depth ordering cues to alter motion interpretation, we included a condition in which the bright bars of the grating were replaced with the same texture used for the flanking regions. This textured grating was presented at zero-disparity and the space-averaged luminance of the textured bars (18 cd/m2) matched the space-averaged luminance of the flanking regions as well as that of the bright bars of the untextured grating. The textured grating moved horizontally leftward or rightward. The texture disambiguated the motion of the grating, which we predicted would override the ability of the depth-ordering cues to alter motion interpretation.

Barber-diamond stereopair

A more accurate representation of the luminance relationships in our barber-diamond stimuli is presented at right. Cross-fuse the stereo pair to view the demo.

Textured barber-diamond

A more accurate representation of the luminance relationships in our textured barber-diamond stimuli is presented at right. Cross-fuse the stereo pair to view the demo.