Abstract
Perceived roughness is associated with a variety of physical factors and multiple peripheral afferent types. The current study investigated whether this complexity of the mapping between physical and perceptual space is reflected at the cortical level. In an integrative psychophysical and imaging approach, we used dot pattern stimuli for which previous studies reported a simple linear relationship of interdot spacing and perceived spatial density and a more complex function of perceived roughness. Thus, by using both a roughness and a spatial estimation task, the physical and perceived stimulus characteristics could be dissociated, with the spatial density task controlling for the processing of low-level sensory aspects. Multivoxel pattern analysis was used to investigate which brain regions hold information indicative of the level of the perceived texture characteristics. While information about differences in perceived roughness was primarily available in higher-order cortices, that is, the operculo-insular cortex and a ventral visual cortex region, information about perceived spatial density could already be derived from early somatosensory and visual regions. This result indicates that cortical processing reflects the different complexities of the evaluated haptic texture dimensions. Furthermore, this study is to our knowledge the first to show a contribution of the visual cortex to tactile roughness perception.
Highlights
The way we interact with objects in our environment is partly determined by material properties such as texture
The comparison of high versus low density trials in the density rating task revealed significantly lower activations for high density trials in the ipsilateral postcentral gyrus (PoCG) extending into the postcentral sulcus (PoCS; peak voxel: t(20184) = −4.43, P < 0.001), including Brodmann’s area 1 (BA1)
Significant above-chance classification was confirmed for the lateral prefrontal cortex (58.9%, chance level: 51.7%, P = 0.008), the posterior occipital cortex (56.1%, chance level: 51.6%, P = 0.012), and the ventral temporal cortex (VTC) (56.2%, chance level: 51.4%, P = 0.024)
Summary
The way we interact with objects in our environment is partly determined by material properties such as texture. Texture is a multidimensional construct and can be described by several perceptual attributes such as rough, dense, soft, slippery, and thick (Lederman et al 1986; Hollins et al 1993, 2000; Picard et al 2003; Gescheider et al 2005; Bergmann Tiest and Kappers 2006). Physical roughness can be described as being associated with several physical stimulus properties, including height differences, spatial properties of the texture (e.g., the spacing between single texture elements), and friction (Bergmann Tiest 2010). The effect of these factors on perceived surface roughness has been investigated and confirmed in numerous studies Roughness perception is very likely influenced by a combination of different physical factors
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