Shape adaptation exaggerates shape differences.

Area of Science:

• Visual perception
• Cognitive psychology
• Neuroscience

Background:

• Perceptual aftereffects vary, with some (e.g., color) involving recalibration against environmental norms.
• Other aftereffects, like those in spatial vision, may use contrastive processes, exaggerating stimulus differences.
• The underlying mechanism for shape aspect ratio aftereffects remains debated.

Purpose of the Study:

• To determine if recalibrative or contrastive processes drive the shape aspect ratio aftereffect.
• To investigate the role of norm-referenced representations in spatial adaptation.
• To understand how adaptation influences the perception of shape and novelty.

Main Methods:

• Three experiments investigated adaptation to different shape aspect ratios.
• Participants adapted to moderately elongated shapes and circles.
• Perceived aspect ratios of test shapes were measured after adaptation.

Main Results:

• Adaptation to an elongated shape compressed perception of narrower shapes and elongated perception of wider shapes.
• Adaptation did not alter the perceived aspect ratio of the adaptor stimulus itself.
• Adapting to a circle produced bidirectional aftereffects on shapes of varying aspect ratios.
• Results ruled out explanations based on local edge orientation or single dimensions.

Conclusions:

• Shape aspect ratio aftereffects are driven by contrastive processes, not recalibration.
• These findings suggest adaptation enhances novelty detection rather than adjusting a norm.
• The visual system exaggerates differences between successive stimuli, influencing shape perception.