Inverse effectiveness in the left but not right lateral occipital cortex during visuo-haptic object categorization
Sunah Kim, Daniel Eylath, Ryan Stevenson, Aaron Scott, Thomas James
Poster
Time: 2009-07-01 09:00 AM – 10:30 AM
Last modified: 2009-06-04
Abstract
Purpose of the Study. There are many studies that have investigated the neural substrates involved in visuo-haptic object recognition, but few, if any, have assessed whether or not the cortical sites implicated in visuo-haptic object recognition show evidence of neuronal convergence. In a previous study, using an additive-factors design, we found evidence for neuronal convergence in three distinct object-selective brain regions in the left hemisphere. In that study, participants touched objects, viewed pictures of objects, and simultaneously touched objects while viewing pictures. Although the pictures were of the same objects that they were touching, the procedure led to incongruencies in spatial location and temporal synchrony of visual and haptic object exploration. The present study used the same additive-factors design, but with a more “ecological� procedure, where participants were able to view their hand touching the objects through a mirror. The additive-factor in this study was ‘difficulty’ instead of ‘stimulus saliency’, which was varied by changing the similarity of objects in a two-alternative forced-choice (2AFC) task.
Methods. Fourteen volunteers (seven females, age 20-34, right-handed) participated. All participants were familiarized with the task before imaging. All objects were tangible and made of ABS plastic. Object-selective brain regions were functionally localized in individual participants by a contrast of visual objects with visual textures in conjunction with a contrast of haptic objects with haptic textures. In the second phase of the study, participants were presented with objects, and asked to make a 2AFC for whether the object was more square or more round. Difficulty of the task was manipulated across runs by changing the similarity of the curvature of the two objects. Participants viewed the objects without touching (V), touched the objects without opening their eyes (H), or viewed their hand touching the object (VH).
Results. Bi-modal object-selective regions-of-interest (ROI) were more reliably found in the left hemisphere (LH; N=11) than right (RH; N=8). Difficulty level had a significant effect on BOLD activation in the left lateral occipital tactile-visual area (LOtv) with the uni-sensory conditions (V & H). As difficulty increased, activation decreased (Figure 1). This effect was weaker with the multisensory visuo-haptic condition (VH). To assess neuronal convergence in left LOtv with the additive-factors design, we calculated BOLD differences between high-difficulty and low-difficulty conditions (Figure 2). ΔVH was significantly less than the sum of ΔV and ΔH, suggesting that visual and haptic sensory channels are integrated in left LOtv. Multisensory gain in left LOtv increased with decreasing effectiveness, an effect called inverse effectiveness. The same ROI analysis in right LOtv showed no evidence for neuronal convergence (Figure 2). A whole-brain SPM analysis found evidence of inverse effectiveness in other regions, including the intraparietal sulcus, parietal operculum, and fusiform gyrus, all in the LH.
Conclusions. Using this more “ecological� procedure, activation during visuo-haptic object categorization showed a pattern of inverse effectiveness, which is consistent with established principles of multisensory integration. Although both left and right LOtv areas were recruited for the visuo-haptic object recognition, only left LOtv showed evidence of multisensory integration.
Methods. Fourteen volunteers (seven females, age 20-34, right-handed) participated. All participants were familiarized with the task before imaging. All objects were tangible and made of ABS plastic. Object-selective brain regions were functionally localized in individual participants by a contrast of visual objects with visual textures in conjunction with a contrast of haptic objects with haptic textures. In the second phase of the study, participants were presented with objects, and asked to make a 2AFC for whether the object was more square or more round. Difficulty of the task was manipulated across runs by changing the similarity of the curvature of the two objects. Participants viewed the objects without touching (V), touched the objects without opening their eyes (H), or viewed their hand touching the object (VH).
Results. Bi-modal object-selective regions-of-interest (ROI) were more reliably found in the left hemisphere (LH; N=11) than right (RH; N=8). Difficulty level had a significant effect on BOLD activation in the left lateral occipital tactile-visual area (LOtv) with the uni-sensory conditions (V & H). As difficulty increased, activation decreased (Figure 1). This effect was weaker with the multisensory visuo-haptic condition (VH). To assess neuronal convergence in left LOtv with the additive-factors design, we calculated BOLD differences between high-difficulty and low-difficulty conditions (Figure 2). ΔVH was significantly less than the sum of ΔV and ΔH, suggesting that visual and haptic sensory channels are integrated in left LOtv. Multisensory gain in left LOtv increased with decreasing effectiveness, an effect called inverse effectiveness. The same ROI analysis in right LOtv showed no evidence for neuronal convergence (Figure 2). A whole-brain SPM analysis found evidence of inverse effectiveness in other regions, including the intraparietal sulcus, parietal operculum, and fusiform gyrus, all in the LH.
Conclusions. Using this more “ecological� procedure, activation during visuo-haptic object categorization showed a pattern of inverse effectiveness, which is consistent with established principles of multisensory integration. Although both left and right LOtv areas were recruited for the visuo-haptic object recognition, only left LOtv showed evidence of multisensory integration.