Neural Basis of Haptic Object Processing, The

Canadian Journal of Experimental Psychology,  Sep 2007  by James, Thomas W,  Kim, Sunah,  Fisher, Jerry S

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Based on the neuroimaging evidence, there are other brain areas that have been implicated in haptic shape processing. One of these areas is the anterior aspect of the intraparietal sulcus (aIPS; Figure 2). In three studies, area aIPS produced greater activation with length or shape discriminations than with roughness discriminations (Bodegard et al., 2001; Kitada et al., 2006; Roland et al., 1998). However, two other studies that made similar comparisons did not find activation in area aIPS (Servos et al., 2001; Stoesz et al., 2003). One potential reason for this discrepancy involves findings from another group of studies (Binkofski, Buccino, Posse et al., 1999; Binkofski, Buccino, Stephan et al., 1999; Binkofski et al., 1998) that investigated the neural mechanisms of haptic object recognition from a slightly different perspective, namely, that haptic exploration requires a unique interaction between somatosensory and motor systems. The conclusion they draw from their findings is that aIPS is not a purely somatosensory processing region, but instead integrates somatosensory and motor information. This conclusion is supported by neuropsychological findings; patients with damage in the aIPS region of the parietal lobe suffer from tactile apraxia, which is characterized by an inability to recognize objects haptically due to inappropriate use of exploratory movements (Binkofski, Kunesch, Classen, Seitz, & Freund, 2001; Binkofski et al., 1998; Pause, Kunesch, Binkofsky, & Freund, 1989).

The sensorimotor nature of aIPS is not its only intriguing feature; other neuroimaging and neurophysiologic studies suggest that aIPS is actually a bimodal sensory region that also receives inputs from the visual system (Culham & Kanwisher, 2001; Grefkes, Weiss, Zilles, & Fink, 2002; Zhang, Weisser, Stilla, Prather, & Sathian, 2004). There is evidence that aIPS is involved in mental rotation of both visually and tactilely presented stimuli (Alivisatos & Petrides, 1996; Prather, Votaw, & Sathian, 2004). Also, visually, area aIPS is thought to process shape information for the purpose of generating and executing goal-directed actions such as visually guided reaching and grasping movements (James, Culham, Humphrey, Milner, & Goodale, 2003). Thus, aIPS may be a site of convergence for several interrelated sensorimotor processes that rely on visual, haptic and motor information to analyze object shape.

Another brain area implicated in haptic shape processing, based on neuroimaging evidence, is LOtv (Figure 2). Several neuroimaging studies have found evidence that LOtv is activated more by object exploration than by a variety of control conditions (Amedi, Jacobson, Hendler, Malach, & Zohary, 2002; Amedi, Malach, Hendler, Peled, & Zohary, 2001; James et al., 2002; Peltier et al., 2007; Pietrini et al, 2004; Prather et al., 2004; Reed et al., 2004; Stoesz et al., 2003; Zhang et al., 2004). Five of these studies (James et al., 2002; Peltier et al., 2007; Prather et al., 2004; Stoesz et al., 2003; Zhang et al., 2004) used objects that could not be distinguished based on their material properties, that is, they could only be distinguished based on their shape, suggesting that LOtv is involved in shape processing, but may not be involved in processing other characteristics of objects. Area LOtv is part of a larger complex of visual processing areas called the lateral occipital complex (Malach et al., 1995). Many neuroimaging studies have found that LOtv, like the neighbouring areas, is activated by visual input (Amedi et al., 2001; James et al., 2002; Peltier et al., 2007; Pietrini et al., 2004; Stoesz et al., 2003; Zhang et al., 2004); therefore, like aIPS, LOtv is bimodal and involved in processing visual and haptic shape information about objects.