Uncovering the Role of the Early Visual Cortex in Visual Mental Imagery

Abstract

The question of whether the early visual cortex (EVC) is involved in visual mental imagery remains a topic of debate. In this paper, I propose that the inconsistency in findings can be explained by the unique challenges associated with investigating EVC activity during imagery. During perception, the EVC processes low-level features, which means that activity is highly sensitive to variation in visual details. If the EVC has the same role during visual mental imagery, any change in the visual details of the mental image would lead to corresponding changes in EVC activity. Within this context, the question should not be whether the EVC is 'active' during imagery but how its activity relates to specific imagery properties. Studies using methods that are sensitive to variation in low-level features reveal that imagery can recruit the EVC in similar ways as perception. However, not all mental images contain a high level of visual details. Therefore, I end by considering a more nuanced view, which states that imagery can recruit the EVC, but that does not mean that it always does so.

Keywords: early visual cortex; mental imagery; visual perception.

Figure 1

Challenging properties of early visual cortex (EVC) activity during imagery. (A) Activity in the EVC is highly sensitive to changes in low-level features, such as where in visual space a stimulus is located. Top row indicates toy visual signals, spreading over the visual field. Bottom row indicates the activity pattern in a grid of EVC neurons. (B) Imagery is thought to be instantiated through inhibitory feedback connections, leading to the sharpening of representations rather than increases in general activation levels. This means that the EVC can still be involved in imagery even if there is no change or even a decrease in general activation.