Neural activity in human visual cortex is transformed by learning real world size

Abstract

The way that our brain processes visual information is directly affected by our experience. Repeated exposure to a visual stimulus triggers experience-dependent plasticity in the visual cortex of many species. Humans also have the unique ability to acquire visual knowledge through instruction. We introduced human participants to the real-world size of previously unfamiliar species, and to the functional motion of novel tools, during a functional magnetic resonance imaging scan. Using machine learning, we compared activity patterns evoked by images of the new items, before and after participants learned the animals' real-world size or tools' motion. We found that, after acquiring size information, participants' visual activity patterns for the new animals became more confusable with activity patterns evoked by similar-sized known animals in early visual cortex, but not in ventral temporal cortex, reflecting an influence of new size knowledge on posterior, but not anterior, components of the ventral stream. In contrast, learning the functional motion of new tools did not lead to an equivalent change in recorded activity. Finally, the time-points marked by evidence of new size information in early visual cortex were more likely to show size information and greater activation in the right angular gyrus, a key hub of semantic knowledge and spatial cognition. Overall, these findings suggest that learning an item's real-world size by instruction influences subsequent activity in visual cortex and in a region that is central to semantic and spatial brain systems.

Keywords: Animacy; Concepts; Learning; Memory; Size; Vision.

Figure 1:. Example stimuli for the four unfamiliar items.

Top left: echidna; bottom left: tapir; top right: pump-drill; bottom right: wood plane.

Figure 2:. An overlap map of participants’ top 200 VT features.

A searchlight was used to classify animals from tools in each participant’s VT cortex. The central voxels of the top 200 searchlights were then used as features. The color scale reflects the number of participants with each voxel as a feature. Brain image Talairach coordinates: 32x, −46y, −13z.

Figure 3:. Decoding new and matched familiar animals and tools before and after learning.

Left:Regions-of-interest shown in a transparent brain, with early visual cortex (EVC) depicted in blue and ventral temporal (VT) cortex shown in red. Right top row: Classification performance at discriminating size-matched new and familiar species decreased in EVC and increased in VT cortex after learning. An asterisk indicates a significant difference (p < 0.05) in a two-tailed paired t-test. Right bottom row: Classification performance at discriminating the new and motion-matched familiar tools in EVC and VT cortex did not change after learning.