New directions in touch.

Abstract

The purpose of this special issue on New Directions in Touch is to focus the spotlight on a number of critical topics concerning the sense of touch, with invited reviews written by some of the top researchers in the field today. Some of these are traditional topics that have seen impressive advances in recent years, while others are quite new. Our intent in highlighting this work is to reflect the increasing excitement in recent years surrounding the exponential increase in highly innovative and diverse research devoted to the sense of touch. There are a total of nine articles in this special issue of the Canadian Journal of Experimental Psychology. Collectively, they cover a wide assortment of topics related to human tactile and haptic sensing and its application, including sensation, perception, cognition and their underlying neural mechanisms, and how basic research on touch has been applied to the design of haptic interfaces for teleoperation and virtual environments. Many different methodologies have been employed in this research, including psychophysics, a variety of perceptual and cognitive behavioural paradigms, single-unit recording, fMRI, and examination of neurologically impaired populations and neuropsychology case studies. The papers also report on methods used by mechanical engineers and computer scientists to design haptic interfaces (hardware and software systems) for use in a wide range of teleoperation and virtual-environment application domains. McGlone, Vallbo, Olausson, Loken, and Wessberg discuss a new submodality of the cutaneous system, in addition to those long established and consisting of touch, temperature, itch, and pain. They propose that this recently discovered tactile submodality is found only in hairy skin, and that it serves the function of affiliative or emotional (pleasant) touch. In their article, McGlone et al. review the peripheral and central neural mechanisms of pleasant touch and compare them to those related to discriminative touch. Hollins and Bensmaia carefully describe how the somatosensory system extracts, encodes, and processes surface roughness and smoothness, two of the most comprehensively studied components of surface texture to date. They propose an elegant model of the roughness perception of fine and coarse surfaces, involving two coding mechanisms and subserved by two populations of tactile afferents and their central connections. The model is strongly supported by a series of very clever psychophysical experiments. Spence and Gallace consider evidence that reveals that it is possible to direct one’s attention to the tactile modality or to the region of space where tactile stimuli are delivered via voluntary (endogenous/top-down) or reactive (exogenous/bottom-up) orienting. These authors present the most recent research on the interaction between these two modes of attention, as well as on tactile numerosity judgments and change detection, highlighting substantial cognitive (attentional) restrictions that may limit people’s ability to process more complex tactile displays. Kappers tackles the challenging topic of how people encode space through haptic exploration. A highly comprehensive series of psychophysical experiments reveal impressively large systematic errors in all experimental conditions. These data lead to a model of haptic space perception in which an egocentric reference frame biases judgments of allocentric space. The roles of hand-centred and body-centred egocentric frames of reference are both considered. James, Kim, and Fisher address the neural organization of haptic object processing, focusing primarily on the object properties of shape and material. They propose two separate hierarchically organized neural pathways, one for processing material properties, such as texture, via cortical regions in SI and SII, and another for processing object shape. Paralleling the neural organization of the visual system, the haptic system is further broken down into dorsal and ventral streams for purposes of action and perception, respectively. Lederman, Kilgour, Kitada, Klatzky, and Hamilton summarize a new body of research on face processing, which indicates that both facial identity and universal facial expressions of emotion can be haptically processed at levels well above chance. Their research adopts a set of converging methodologies, including behavioural paradigms with both neurologically intact