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The crossmodal congruency task (CCT) is a commonly used paradigm for measuring visual–tactile interactions and how these may be influenced by discrepancies in space and time between the tactile target and visual distractors. The majority of studies which have used this paradigm have neither measured, nor attempted to control, individual variability in unisensory (tactile) performance. We have developed a version of the CCT in which unisensory baseline performance is constrained to enable comparisons within and between participant groups. Participants were instructed to discriminate between single and double tactile pulses presented to their dominant hand, at their own approximate threshold level. In Experiment 1, visual distractors were presented at −30 ms, 100 ms, 200 ms and 400 ms stimulus onset asynchronies. In Experiment 2, ipsilateral visual distractors were presented 0 cm, 21 cm, and 42 cm vertically from the target hand, and 42 cm in a symmetrical, contralateral position. Distractors presented −30 ms and 0 cm from the target produced a significantly larger congruency effect than at other time points and spatial locations. Thus, the typical limits of visual–tactile interactions were replicated using a version of the task in which baseline performance can be constrained. The usefulness of this approach is supported by the observation that tactile thresholds correlated with self-reported autistic traits in this non-clinical sample. We discuss the suitability of this adapted version of the CCT for measuring visual–tactile interactions in populations where unisensory tactile ability may differ within and between groups.

Reaching and grasping requires integration of visual, proprioceptive and somatosensory inputs. Previous research has shown that manipulating the ‘graspabilty’ of a visual stimulus influences reaction times to that stimulus (e.g., Tucker and Ellis, 1998). Here we explored whether this same effect can be extended to the planning and online control of arm movements. Participants made a mimed reaching movement with their left or right hand depending on the colour of images of affordance (door handles) and control stimuli (a row of dots of similar size and orientation as the door handle). Stimulus onset was manipulated by changing when the grey stimulus changed colour. Stimuli either pointed towards (compatible) or pointed away from (incompatible) the responding hand. Spatially compatible affordance stimuli facilitated reach onset compared to other stimuli and compatibility combinations, replicating previous reaction time studies. This can be attributed to a priming of the motor system by spatially compatible affording items. Results also indicated a larger outwards deviation of reach trajectory for spatially incompatible control stimuli compared to spatially compatible control stimuli, which waned with stimulus onset delay. This reveals an immediate inhibitory effect on reach trajectory, such that outwards movement is over-compensated to negate this incompatible orientation. Overall, we observed that the effect of visual spatial compatibility on reach kinematics differs with the action relevance of the stimulus. We are currently exploring how this multisensory visuomotor effect changes with age.

Studies into tactile detection have found that a simultaneous light stimulus affects judgments of the presence or absence of a near threshold tactile stimulus, leading to higher numbers of false alarms, whereby participants report feeling a touch in the absence of a stimulus, as well as modest improvements in tactile sensitivity (Lloydet al., 2008; McKenzieet al., 2010, 2012). Anecdotally, the reported intensity of the bi-modal stimuli was also enhanced — an effect that was investigated in the current studies. In Experiment 1 participants discriminated between ‘weak’ and ‘strong’ tactile stimuli, which were accompanied by a light flash on 50% of trials. We observed a bias towards classifying light-present vibrations as ‘strong’ regardless of signal strength, as well as some evidence for improved accuracy in discrimination. In Experiment 2, participants gave a subjective intensity rating on a 6-point scale, which showed an increase in magnitude ratings for both ‘weak’ and ‘strong’ vibrotactile stimuli when the light was present. This shows that a simultaneous light can both improve tactile discrimination and lead to both types of tactile stimulus being rated as stronger. Primary somatosensory cortex may underlie these effects, as it receives direct projections from visual cortex and indirect projections from association areas of the brain. However, it is as yet unclear whether or not these effects are due to the same underlying mechanism, or at which processing stage they occur. Therefore, we are currently exploring the neural underpinnings of this amplification effect using both fMRI and EEG.