Chapter 1. Center-Surround Illusions

1.1 Introduction

One of the main conclusions from the center-surround receptive fields experiment is that these receptive fields are more sensitive to the changes in light levels at the edges where light levels change than to the absolute level of light. This finding has been used to explain several visual illusions, such as the Mach Bands shown below.

The dark bar at the yellow arrow and the bright bar at the red arrow do not actually exist (Cornsweet, 1970). They are caused by the reaction of the receptive fields at the edges where these bars occur. Another illusion explained by these center-surround receptive fields is the well-known Hermann grid shown below.

The intersections of the white lines look dark and reflect the greater inhibition of cells positioned at the intersection than those positioned along the lines away from the intersection.

In this experiment, you will examine another illusion attributed to these center-surround receptive fields and see what happens.

Cornsweet, T. N. (1970). Visual Perception. New York: Academic Press.

Enroth-Cugell, C. & Robson, J. (1966). The contrast sensitivity of retinal ganglion cells of the cat. Journal of Physiology, 187, 517-566.

Kuffler, S. W. (1953). Discharge patterns and functional organization of mammalian retina. Journal of Neurophysiology, 16, 37-68.

1.2 Experiment Setup

Figure 1.3

1.3 Instructions

Your task is to match the two center squares. At the beginning of each trial, the brightness of the square on the right will be one of a large number of random brightnesses. Below the white square will be a + button, which will make the square brighter and a – button, which will make the square darker. When you are done adjusting the brightness, press the Match button.

1.4 Experiment

Figure 1.5

1.5 Results

Figure 1.6

1.6 Quiz