Abstract
We investigated the neural underpinnings of texture categorisation using exemplars that were previously learned either within modalities (visual training and visual test) or across modalities (tactile training and visual test). Previous models of learning suggest a decrease in activation in brain regions that are typically involved in cognitive control during task acquisition, but a concomitant increase in activation in brain regions associated with the representation of the acquired information. In our study, participants were required to learn to categorise fabrics of different textures as either natural or synthetic. Training occurred over several sessions, with each fabric presented either visually or through touch to a participant. Pre- and post-training tests, in which participants categorised visual images only of the fabrics, were conducted during a functional magnetic resonance imaging (fMRI) scan. Consistent with previous research on cognitive processes involved in task acquisition, we found that categorisation training was associated with a decrease in activation in brain regions associated with cognitive systems involved in learning, including the superior parietal cortex, dorsal anterior cingulate cortex (dACC), and the right dorsolateral prefrontal cortex (DLFC). Moreover, these decreases were independent of training modality. In contrast, we found greater activation to visual textures in a region within the left medial occipital cortex (MOC) following training. There was no overall evidence of an effect of training modality in the main analyses, with texture-specific regional changes associated with both within- (visual) and cross- (touch) modal training. However, further analyses suggested that, unlike categorisation performance following within-modal training, crossmodal training was associated with bilateral activation of the MOC. Our results support previous evidence for a multisensory representation of texture within early visual regions of the cortex and provide insight into how multisensory categories are formed in the brain.
Highlights
The issue of how sensory information is organised into different categories has received considerable interest in the literature, with regards to object shapes (Riesenhuber and Poggio, 1999; Newell and Bülthoff, 2002), faces and facial expressions (Calder et al, 1996; Bülthoff and Newell, 2004) and scenes (Thorpe et al, 1996; Greene et al, 2016)
The task was more difficult in the tactile modality (56.3 and 69.2% accuracy in Block 1 for touch and vision, respectively) there was evidence of improvement in both modalities: performance following training in the tactile modality improved by 7.5% (SD = 14.75%) whilst performance in the visual modality improved by 14.2% (SD = 6.45%)
These pre- and post-training tests were conducted within the scanner, and in the visual modality only
Summary
The issue of how sensory information is organised into different categories has received considerable interest in the literature, with regards to object shapes (Riesenhuber and Poggio, 1999; Newell and Bülthoff, 2002), faces and facial expressions (Calder et al, 1996; Bülthoff and Newell, 2004) and scenes (Thorpe et al, 1996; Greene et al, 2016). A Labrador belongs to the category of ‘dog’ on the basis of multisensory information including visual information about its shape and size, as well as other non-visual information such as the sound of the dog barking, the feel of its coat and maybe even its smell Despite this sensory convergence, the cognitive and cortical processes underpinning the formation of multisensory categories is poorly understood. The task of categorisation itself involves learning to associate particular features of an object with belonging to a particular category Such a skill is likely to be domain general, and non-specific to different category types. We used neuroimaging to investigate the role of higher-level cognitive and lower-level perceptual processes involved in learning to categorise novel textures and ask whether these processes may be specific to, or independent of, the learning modality
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