Beyond shape: how you learn about objects affects how they are represented in visual cortex

Abstract

Background: Experience can alter how objects are represented in the visual cortex. But experience can take different forms. It is unknown whether the kind of visual experience systematically alters the nature of visual cortical object representations.

Methodology/principal findings: We take advantage of different training regimens found to produce qualitatively different types of perceptual expertise behaviorally in order to contrast the neural changes that follow different kinds of visual experience with the same objects. Two groups of participants went through training regimens that required either subordinate-level individuation or basic-level categorization of a set of novel, artificial objects, called "Ziggerins". fMRI activity of a region in the right fusiform gyrus increased after individuation training and was correlated with the magnitude of configural processing of the Ziggerins observed behaviorally. In contrast, categorization training caused distributed changes, with increased activity in the medial portion of the ventral occipito-temporal cortex relative to more lateral areas.

Conclusions/significance: Our results demonstrate that the kind of experience with a category of objects can systematically influence how those objects are represented in visual cortex. The demands of prior learning experience therefore appear to be one factor determining the organization of activity patterns in visual cortex.

Figure 1. The artificial objects (Ziggerins) and training tasks.

(a). The entire Ziggerin set of seventy-two novel objects. The six classes were shown in separate rows. (b). Individuation training consisted of three tasks: naming, verification, and matching. (c). Categorization training consisted of the naming and verification tasks, as well as a matrix scanning task with an example trial shown.

Figure 2. An example scan of the fMRI pre- and post-training scans.

In the within-class discrimination condition, each block contained only Ziggerins within the same class, thus requiring within-class/subordinate-level discrimination. In the between-class discrimination condition, each block contained Ziggerins from different classes, thus requiring between-class/basic-level discrimination. The control blocks contained familiar objects from different categories.

Figure 3. Training effects in the group-defined face-selective, right fusiform region (Talairach coordinates: 40, −44, −18).

(a). Activity changes (post minus pre) for Ziggerins during within- and between-class discrimination after individuation vs. categorization training. Error bars represent the 95% confidence intervals for group differences. (b). Correlations between training-induced activity changes in this right fusiform region for the Ziggerins and the configural processing effect found for the Ziggerins measured behaviorally.

Figure 4. Training effects for the ventral occipito-temporal regions.

The categorization group showed increased activity for the Ziggerins in the medial regions and decreased activity at the lateral regions after training, as indicated by the significance of the linear trends within each hemisphere (p<.05, .01, and .001 indicated by one, two, and three asterisks respectively). The individuation group did not show any reliable pattern of changes. The brain was depicted with a radiological convention (i.e., left hemisphere one the right).