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In the main experiment of one study, published at https://doi.org/10.1101/2022.10.13.512071 we used a recalibration protocol that was based on the visuotactile ventriloquism aftereffect applied to 8 landmarks of human participants' left hands. We presented visual stimuli further outwards than the tactile positions. According to the principle of the ventriloquism effect, the visual stimuli should, when integrated with the tactile stimuli, perceptually attract and over longer exposure recalibrate the perceived position of the tactile stimuli. We argued that this outward-recalibration might lead to an increase of the size of a perceptual hand map. We alternated recalibration phases, in which participants merely attended to the visual and tactile stimuli, with localization phases in which participants localized unisensory tactile stimuli by pointing movements on a touch screen mounted above the recalibrated left hand. As a dependent measure, we used the localizations of the unisensory tactile stimuli. We computed distances between the localizations as an expression of hand size (see the manuscript for details). We also assessed tactile distance judgments (TDJ) before and after recalibration as another measure of (implicit) hand size. We observed that localization-based hand size increased and TDJ decreased by recalibration and argued that this is evidence that the recalibration procedure has changed an underlying representation of hand size that influences both behavioral assessments. However, an alternative explanation for (at least the localization) results is that there is no change in an underlying size representation and that all hand landmarks were merely individually recalibrated. To rule out this alternative explanation, we preregister a validation study. In this new experiment, we evoke recalibration with a set of visuotactile landmarks. We then test the localization of these as well as of additional landmarks tactually. The additional landmarks are not part of the recalibration set. If there are localization effects for those landmarks consistent with having pointed to an increased hand size, the result cannot be explained with recalibration of all individual landmarks because some of the tested landmarks were not used during recalibration. Thus, if additional landmarks are affected by the recalibration procedure, it is likely due to an underlying hand size representation.

Any series of sensorimotor actions shows fluctuations in speed and accuracy from repetition to repetition, even when the sensory input and the motor output requirements remain identical over time. Such fluctuations are particularly prominent in reaction time (RT) series from laboratory neurocognitive tasks. Despite their omnipresent nature, trial-to-trial fluctuations remain poorly understood. Here, we systematically analysed RT series from various neurocognitive tasks, quantifying how much of the total trial-to-trial RT variance can be explained by three sources of variability that are frequently investigated in behavioural and neuroscientific research: 1) the experimental conditions, which are commonly employed to induce systematic patterns in variability, 2) short-term temporal dependencies such as the autocorrelation between subsequent trials, and 3) long-term temporal trends over entire experimental blocks and sessions. Furthermore, we examined to what extent the explained variances by these sources are shared or unique. In total, we analysed 1913 unique RT series from 30 different cognitive control and perception-based tasks. On average, the three sources together explained only about 8-17% of the total variance. The experimental conditions explained on average about 2.5-3.5%, but did not share explained variance with temporal dependencies. Thus, the largest part of the trial-to-trial fluctuations in RT remained unexplained by the three variability sources that are typically analysed here. These may be attributable to observable endogenous factors, such as ongoing fluctuations in brain activity and bodily states, though some extent of randomness may be a feature of behaviour rather than just nuisance.

The spatial-size association of response code (SSARC) effect refers to the finding of better performance with the left hand to small stimuli and with the right hand to large stimuli, as compared to the reverse mapping. In the present study, we investigated which response coding is responsible for the emergence of the SSARC effect. We observed a SSARC effect only with response selection between hands but not between fingers of one hand, indicating that the responses are coded relative to the body midline. Further, we observed a SSARC effect with parallel arms but not with crossed arms, suggesting that both the anatomical side of the effector and its external spatial position contribute to the response code. However, using a reaching task as compared to keypresses, the SSARC effect followed the arms, suggesting that the crucial spatial response code refers more strongly to the anatomical side of the effector rather than to the external spatial response position. These findings document a strong influence of anatomically- or body-based coding on the SSARC effect, are at odds with the proposition of a generalized magnitude system that utilizes a common, external-spatial metric, and point toward a categorical nature of response codes underlying the SSARC.

Visuospatial attention is a prerequisite for the performance of visually guided movements: Perceptual discrimination is regularly enhanced at target locations prior to movement initiation. It is known that this attentional prioritization evolves over the time of movement preparation; however, it is not clear whether this build-up simply reflects a time requirement of attention formation or whether, instead, attention build-up reflects the emergence of the movement decision. To address this question, we combined behavioral experiments, psychophysics, and computational decision-making models to characterize the time course of attention build-up during motor preparation. Participants (n = 46, 29 female) executed center-out reaches to one of two potential target locations and reported the identity of a visual discrimination target that occurred concurrently at one of various time-points during movement preparation and execution. Visual discrimination increased simultaneously at the two potential target locations but was modulated by the experiment-wide probability that a given location would become the final goal. Attention increased further for the location that was then designated as the final goal location, with a time course closely related to movement initiation. A sequential sampling model of decision-making predicted key temporal characteristics of attentional allocation. Together, these findings provide evidence that visuospatial attentional prioritization during motor preparation does not simply reflect that a spatial location has been selected as movement goal, but rather indexes the time-extended, cumulative decision that leads to selection, hence constituting a link between perceptual and motor aspects of sensorimotor decisions.Significance statementWhen humans perform a goal-directed movement such as a reach, attention shifts towards the goal location already before movement initiation, indicating that motor goal selection relies on the use of attention. Here, we demonstrate that key temporal aspects of visuospatial attention are predicted by a well-known computational model of decision-making. These findings suggest that visual attention signals much more than simply that a motor goal has been selected: instead, the time-course of emergent, visuospatial attention reflects the time-extended, cumulative decision that leads to goal selection, offering a window onto the tight link of perceptual and motor aspects in sensorimotor decision-making.

Humans localize touch on hand-held tools by interpreting the unique vibratory patterns elicited by impact to different parts of the tool. This perceptual strategy differs markedly from localizing touch on the skin. A new study shows that, nonetheless, touch location is probably processed similarly for skin and tool already early in somatosensory cortex. Copyright © 2019 Elsevier Ltd. All rights reserved.