The physiology and psychology of selective attention to touch

Abstract

In this chapter we review psychological and physiological experiments on selective attention to touch stimuli. We explore the role of selective attention in tactile target detection and search, determining those tasks that benefit from attention and those which can be effectively performed pre-attentively. We also try to determine the stage at which attentional selection occurs. We review electrophysiological and human brain imaging (PET, fMRI, MEG, SEP) studies to assess how early in the somatosensory processing pathway attentional modulation occurs.There is some evidence that the primary somatosensory cortex (S1) can show attentional effects. However, a number of studies have suggested that there is a hierarchy to attentional modulation in the somatosensory system, with the greatest effects being observed in secondary and association areas. INTRODUCTIONAfter decades of research on selective attention, one of the clearest definitions of attention is still to be found in William James' Principles of Psychology, written in 1890."Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others" (1).It is this ability which allows us to attend to one conversation in a crowded room, blocking out all other noise -the so called 'cocktail party effect'. This voluntary or 'top-down' focussing of attention is distinct from the reflexive or 'bottom up' shifting of attention that occurs when we hear our name in another, unattended conversation. The cocktail party scenario illustrates some of the main issues in attentional research. For exampledoes selective attention to one input lead to increased sensitivity to the attended input? Does the presence of competing conversations affect processing of the attended input? To what level are unattended stimuli processed? This last question is of interest both from the psychological point of view (eg is an unattended word processed to the level of phonology/semantics? (2)) and from the physiological point of view (eg does attention operate at the level of the peripheral receptors, primary sensory cortex or secondary sensory cortices?). This review will attempt to address some of these issues using psychological and physiological evidence from studies of attention and touch.Section 3 provides a brief overview of the anatomy of touch. Particular attention is paid to the question of whether touch processing occurs in series. This is important if we are to relate psychological models of attention (often serial box and arrow models -eg ref 3) to neuroscientific findings.Many studies of selective attention have focussed on the visual system (eg 4-6). It is known that selectively attending to a location in space enhances our perception of visual stimuli appearing at that location (4). However, it is only recently that ...

Correlated neuronal activity and the flow of neural information

“…In these experiments, the firing rates of S2 neurons also varied with attention, consistent with previous reports [99][100][101][102] . About 78% of the neurons showed significant changes in firing rate across conditions, whereas only 11% of all neuron pairs showed significant changes in synchrony 104 .…”

“…Neurons in the secondary somatosensory cortex (S2) respond to tactile stimuli, but are also sensitive to attention [99][100][101] and behavioural context 102 . Motivated by an earlier theoretical proposal 103 , the correlations between pairs of neurons recorded in S2 were analysed as functions of attention 104 .…”

Test–retest study of fMRI signal change evoked by electroacupuncture stimulation

“…This effect may also be related to the well-known finding that attention and arousal can significantly modulate brain response to sensory stimulation including touch and pain (Peyron et al, 1999;Johansen-Berg and Lloyd, 2000;Petrovic et al, 2000;Tracey et al, 2002;Porro et al, 2004). Thus, a subject's level of distraction away from the sensation may influence the amount of activation in some areas of the brain.…”

Independent effects of endogenous and exogenous attention in touch

“…While the majority of experimental studies on spatial attention have been conducted in the visual modality, comparably few studies have investigated tactile attentional selection (see Johansen-Berg & Lloyd, 2000;and Spence & Gallace, 2007, for reviews of tactile attention studies). Furthermore, most studies investigating tactile attention have not controlled for visual orienting effects on tactile processing.…”