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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Before we completely give up on the idea that there could be a separate texture-processing pathway, there is a final group of studies that needs to be addressed. This group of studies used more complicated objects to investigate the neural substrates of haptic object processing. Many of them, however, did not include a texture discrimination condition, or did not fully analyze brain regions that were activated during texture discrimination. On the other hand, some of the studies used objects that could be distinguished using texture, and some of the studies used objects that could not be distinguished using texture; therefore, a comparison of results across studies may be useful.

Three of the studies (Amedi et al., 2001; Pietrini et al., 2004; Reed et al., 2004) compared haptic recognition of real objects with a control condition. Real objects, of course, can be distinguished using all of their many different properties, including material properties such as texture. The results for LOtv showed remarkably consistent results: In all three cases, LOtv produced more activation for haptic object recognition than for the control condition. Two of the three studies (Pietrini et al., 2004; Reed et al., 2004) showed that SII produced more activation for haptic object recognition than for the control condition. Although it was not reported, examination of the activation maps from the third study (Amedi et al., 2001) reveal that SH may have produced consistent results across the studies. The results of these three studies, however, do not distinguish between the processing of different object characteristics; they did not analyze different object characteristics in isolation. Three different studies (James et al., 2002; Peltier et al., 2007; Stoesz et al., 2003) focused on the processing of object shape without texture. Those studies used meaningless objects that were all made from the same material and had the same surface texture; therefore, texture could not be used to distinguish them. These three studies also showed very consistent results: In all cases, area LOtv, but not SII, produced more activation for haptic object recognition than the control condition. A significant difference between the real objects and the meaningless objects in these studies was that the former could be distinguished based on material properties, while the latter could not. One hypothesis based on the comparison of these results is that SII, which only produced activation with the real objects that could be distinguished by texture, is part of a texture processing pathway (Roland et al., 1998). Because the real objects could also be distinguished using several other material properties besides texture, a more general hypothesis would be that SII is a critical stage in a neural pathway for processing material properties.

It should be pointed out that one of the studies (Reed et al., 2004) compared real and meaningless objects directly and found that both SII and LOtv were more strongly activated with real objects than meaningless objects. The meaningless objects in that study differed significantly from the meaningless objects in the other three studies in that they could be distinguished using texture. Thus, the increased activation with real over meaningless objects suggests that activation in SII and LOtv may not be determined only by the ability to distinguish objects based on texture or shape, but may also be influenced by the familiarity of the object.