Ellen Poliakoff

Brief body-scan meditation practice improves somatosensory perceptual decision making.

We have previously found that attention to internal somatic sensations (interoceptive attention) during a heart beat perception task increases the misperception of external touch on a somatic signal detection task (SSDT), during which healthy participants erroneously report feeling near-threshold vibrations presented to their fingertip in the absence of a stimulus. However, it has been suggested that mindful interoceptive attention should result in more accurate somatic perception, due to its non-evaluative and controlled nature. To investigate this possibility, 62 participants completed the SSDT before and after a period of brief body-scan mindfulness meditation training, or a control intervention (listening to a recorded story). The meditation intervention reduced tactile misperception and increased sensitivity during the SSDT. This finding suggests that the perceptual effects of interoceptive attention depend on its particular nature, and raises the possibility that body-scan meditation could reduce the misperception of physical symptoms in individuals with medically unexplained symptoms.

Modulation of saccadic intrusions by exogenous and endogenous attention.

Primary gaze fixation in healthy individuals is frequently interrupted by microsaccades and saccadic intrusions (SI). The neural systems responsible for the control of attention and eye movements are believed to overlap and in line with this, the behaviour of microsaccades appears to be affected by exogenous and endogenous attention shifts. In the current work we wished to establish whether SI would also be influenced by attention in order to provide evidence that SI and microsaccades exhibit similar behaviour and further investigate the extent of overlap between attention and eye movement systems. Twelve participants performed a cue-target task where they were cued exogenously or endogenously and had to respond to the appearance of a peripheral target with either a button press or saccade. Our results replicate earlier microsaccade research, indicating that SI are also influenced by exogenous and endogenous attention. In all conditions, SI frequency initially decreased following the cue, then rose to a maximum before falling to below baseline levels. Following the exogenous cue, SI were more frequently directed away from the cue as predicted by inhibition of return. Additionally, SI direction following the endogenous cue was biased towards the cue for the saccadic response mode only, suggesting that the degree to which the eye movement and attention systems overlap depends on whether an eye movement is required. In summary, our findings indicate that SI characteristics are modulated by exogenous and endogenous attention and in a similar way to microsaccades, suggesting that SI and microsaccades may lie on a continuum of fixational instabilities. Furthermore, as with microsaccades, SI are likely to provide additional insights into the relationship between attention and the oculomotor systems.

Vision and touch in ageing: crossmodal selective attention and visuotactile spatial interactions.

We investigated whether ageing affects crossmodal selective attention (the ability to focus on a relevant sensory modality and ignore an irrelevant modality) and the spatial constraints on such selective processing. Three groups of 24 participants were tested: Young (19-25 years), Young-Old (65-72 years) and Old-Old (76-92 years). The participants had to judge the elevation of vibrotactile targets (upper/index finger and lower/thumb), presented randomly to either hand while ignoring concurrent visual distractors. In a second task, the role of the target and distractor modalities was reversed. Crossmodal selective attention was assessed by comparing performance in the presence versus absence of distractors. Spatial constraints on selective attention were also investigated by comparing the effect of distractors presented on the same versus opposite side as the target. When attending to touch, the addition of visual distractors had a significantly larger effect on error rates in both of the older groups as compared to the Young group. This indicates that ageing has a detrimental effect on crossmodal selective attention. In all three age groups, performance was impaired when the target and distractor were presented at incongruent as compared to congruent elevations in both tasks. This congruency effect was modulated by the relative spatial location of the target and distractor in certain conditions for the Young and the Young-Old group. That is, participants in the two younger age groups found it harder to attend selectively to targets in one modality, when distractor stimuli came from the same side rather than from the opposite side. However, no significant spatial modulation was found in the Old-Old group. This suggests that ageing may also compromise spatial aspects of crossmodal selective attention.

Tactile spatial acuity varies with site and axis in the human upper limb

Historically, beginning with Webers [E.H. Weber, On the sensitivity of the tactile senses, in: H.E. Ross, D.J. Murray (Eds. and Trans.), E.H. Weber on the Tactile Senses, Erlbaum (UK) Taylor & Francis, Hove, 1996 (Original work published in 1834), pp. 21-136] classical studies, regional variations in the accuracy of localisation of tactile stimuli applied to a limb have been recognised. However, important questions remain concerning both the map of localisation resolution and its neuroscientific basis since methodological confounds have militated against an unambiguous, unified interpretation of the diverse findings. To test the hypotheses that localisation precision on the upper limb varies with site (hand, wrist, forearm) and limb axis (transverse, longitudinal), regional differences in locognosic acuity were quantified in psychophysical experiments. Participants identified the perceived direction (e.g. medial or lateral) relative to a central reference locus of brief tactile test stimuli applied to a cruciform array of loci. Acuity was greater in the transverse than longitudinal axis. This effect probably arises from the asymmetry of receptive fields of upper limb first-order sensory units and their higher-order projection neurons. Additionally, acuity was greater on the dorsal surface at the wrist than either the hand or forearm sites, in the longitudinal axis, supporting an enhancement of resolution at joints (anchor points). This effect may contribute to improved proprioceptive guidance of active wrist movements.

Expected taste intensity affects response to sweet drinks in primary taste cortex

Expectations about a food can impact on its taste, but this may represent a perceptual change or a bias in response at the decision-making stage. We hypothesised that expectation of taste intensity should be underpinned by modulation of activity in primary taste cortex. Using functional magnetic resonance imaging, we found that expecting a very sweet drink, but receiving a less sweet drink, enhanced the reported sweetness and bolstered activity in taste cortex, relative to a less sweet drink without this expectation. The activation overlapped with primary taste cortex activation found in 11 recent taste studies. Our findings provide evidence that taste expectation modulates activity in an area consistently reported as primary taste cortex, implying that expectation effects do indeed impact on taste perception.

Goal-directed and goal-less imitation in autism spectrum disorder

To investigate how people with Autism are affected by the presence of goals during imitation, we conducted a study to measure movement kinematics and eye movements during the imitation of goal-directed and goal-less hand movements. Our results showed that a control group imitated changes in movement kinematics and increased the level that they tracked the hand with their eyes, in the goal-less compared to goal-direction condition. In contrast, the ASD group exhibited more goal-directed eye movements, and failed to modulate the observed movement kinematics successfully in either condition. These results increase the evidence for impaired goal-less imitation in ASD, and suggest that there is a reliance on goal-directed strategies for imitation in ASD, even in the absence of visual goals.

Visuotactile temporal order judgments in ageing.

We report an experiment on the effects of ageing on crossmodal temporal perception. Young (mean age = 21.7 years) and old (mean age = 75.1 years) participants were presented with pairs of visual and vibrotactile stimuli to either hand and required to make unspeeded temporal order judgments (TOJs) regarding which sensory modality appeared to have been presented first. The stimulus onset asynchrony (SOA) between the two stimuli was varied using the method of constant stimuli. Temporal precision, as indexed by the just noticeable difference (JND), was better (i.e., JNDs were lower) when the stimuli were presented from different positions (M = 101 ms) rather than from the same position (M = 120 ms), as has been demonstrated previously. Additionally, older observers required more time (i.e., their JNDs were larger) to accurately perceive the temporal order (M = 131 ms) as compared to younger observers (M = 98 ms). Our results confirm that ageing deleteriously affects crossmodal temporal processing even when the spatial confound inherent in previous research has been ruled out.

Illusory touch and tactile perception in somatoform dissociators

OBJECTIVE The psychological mechanisms of somatoform dissociation (i.e., pseudoneurological symptoms) are poorly understood. This study evaluated recent theoretical predictions regarding the role of tactile perception in the development of somatoform dissociative symptoms. METHODS Eighty nonclinical participants scoring either high or low on the Somatoform Dissociation Questionnaire (SDQ-20) completed the Somatic Signal Detection Task (SSDT), a novel perceptual paradigm designed to simulate the occurrence of somatoform symptoms in the laboratory. Prior to the SSDT, participants completed a memory task designed to produce either minimal or maximal activation of tactile representations in memory. RESULTS The high SDQ-20 group exhibited a more liberal response criterion (c) on the SSDT than the low SDQ-20 group after controlling for negative affectivity, somatosensory amplification and depression. This effect was mainly attributable to an increased number of false alarms (i.e., illusory experiences of touch) in the high SDQ-20 group rather than an increased hit rate. General perceptual ability (i.e., tactile sensitivity) was comparable between the two groups. The memory manipulation had no effect on SSDT performance. CONCLUSIONS Somatoform dissociators appear more likely to experience illusory perceptual events under conditions of sensory ambiguity than nondissociators, despite comparable perceptual abilities more generally. These findings support theories that identify distorted perceptual processing as a feature of somatoform dissociation. The SSDT has potential as a tool for further research in this area.

The influence of goals on movement kinematics during imitation

This study took a quantitative approach to investigate movement kinematics during the imitation of goal-directed and non-goal directed movements. Motion tracking equipment was used to record the hand movements of 15 healthy participants during an imitation task involving aiming movements that varied in speed. We predicted that movement kinematics would be most similar to the observed movements in the non-goal condition, as a result of direct visuomotor mapping of the action, and least similar in the goal-directed condition because more importance would be given to the end goal. We also predicted that precues (prior information about the movement) would increase imitation accuracy in the non-goal condition by reducing cognitive demand, and that precues would reduce accuracy in the goal-directed condition, as less attention would be paid to the movement. Results showed that imitation was modulated by the speed of the observed action in the non-goal condition only. Contrary to predictions, precues did not improve imitation in the non-goal condition or improve imitation accuracy in the goal-directed condition. These results demonstrate that visuomotor mapping is favoured in non-goal imitation, regardless of prior information, and that accurate imitation of movement detail is compromised by the presence of goals. Such differences in movement kinematics indicate that different processes mediate the imitation of non-goal and goal-directed actions.

The effect of visual threat on spatial attention to touch

Viewing a threatening stimulus can bias visual attention toward that location. Such effects have typically been investigated only in the visual modality, despite the fact that many threatening stimuli are most dangerous when close to or in contact with the body. Recent multisensory research indicates that a neutral visual stimulus, such as a light flash, can lead to a tactile attention shift towards a nearby body part. Here, we investigated whether the threat value of a visual stimulus modulates its effect on attention to touch. Participants made speeded discrimination responses about tactile stimuli presented to one or other hand, preceded by a picture cue (snake, spider, flower or mushroom) presented close to the same or the opposite hand. Pictures of snakes led to a significantly greater tactile attentional facilitation effect than did non-threatening pictures of flowers and mushrooms. Furthermore, there was a correlation between self-reported fear of snakes and spiders and the magnitude of early facilitation following cues of that type. These findings demonstrate that the attentional bias towards threat extends to the tactile modality and indicate that perceived threat value can modulate the cross-modal effect that a visual cue has on attention to touch.