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The spatial feature underlying the shape-frequency and shape-amplitude after-effects.

Elena Gheorghiu¹, Frederick A A Kingdom

¹McGill Vision Research, Department of Ophthalmology, McGill University, 687 Pine Avenue West, Montreal, Quebec, Canada H3A 1A1. elena.gheorghiu@mcgill.ca

Vision Research

|February 13, 2007

Summary

The shape-frequency after-effect (SFAE) and shape-amplitude after-effect (SAAE) are caused by adapting to local curvature. This suggests intermediate-level visual mechanisms in area V4 process contour shapes.

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Area of Science:

Visual perception
Neuroscience
Computational vision

Background:

Shape after-effects, including shape-frequency and shape-amplitude after-effects (SFAE and SAAE), involve perceptual shifts after adapting to visual contours.
These after-effects typically manifest as a shift away from the adapting stimulus's characteristics.

Purpose of the Study:

To investigate the specific spatial features underlying the SFAE and SAAE.
To determine whether adaptation targets local orientation, average unsigned curvature, periodicity/density, shape-amplitude, or local curvature.

Main Methods:

Employing diverse experimental procedures to test adaptation effects.
Analyzing the relationship between adapting stimulus features and the magnitude of the after-effect.

Main Results:

Results indicate that local curvature is the primary spatial feature responsible for both SFAE and SAAE.
The after-effect magnitude peaked when the test contour presented half a cycle (cosine phase).

Conclusions:

The SFAE and SAAE are likely mediated by neural mechanisms encoding contour fragments with consistent curvature signs.
Area V4 is proposed as the neural substrate, given its role in processing constant sign curvature information.