Generalized movement representation in haptic perception.

Abstract

The extraction of spatial information by touch often involves exploratory movements, with tactile and kinesthetic signals combined to construct a spatial haptic percept. However, the body has many tactile sensory surfaces that can move independently, giving rise to the source binding problem: when there are multiple tactile signals originating from sensory surfaces with multiple movements, are the tactile and kinesthetic signals bound to one another? We studied haptic signal combination by applying the tactile signal to a stationary fingertip while another body part (the other hand or a foot) or a visual target moves, and using a task that can only be done if the tactile and kinesthetic signals are combined. We found that both direction and speed of movement transfer across limbs, but only direction transfers between visual target motion and the tactile signal. In control experiments, we excluded the role of explicit reasoning or knowledge of motion kinematics in this transfer. These results demonstrate the existence of 2 motion representations in the haptic system-one of direction and another of speed or amplitude-that are both source-free or unbound from their sensory surface of origin. These representations may well underlie our flexibility in haptic perception and sensorimotor control. Public Significance StatementHaptic perception or active touch involves 2 types of sensory signals: tactile sensations and proprioceptive or motor signals about the movement of the fingertip or other sensory surface. While these signals usually come from the same limb, we have recently shown that tactile signals from 1 hand can be combined with proprioceptive movement information from the other hand, a phenomenon that we call "haptic transfer." Here we extend these results by showing that haptic transfer can occur between the feet and hands. Additionally, movement signals in haptic transfer can even come from eye movements or visual motion, but in this case less information is transferred than between limbs. These results indicate that, in haptic perception, information about the movement of the sensory surface is represented in a simplified way, without reference to the actual body part involved. Additionally, our results indicate that signals about movement direction might be represented differently than those about speed.

Radial trunk-centred reference frame in haptic perception

“…The median score over subjects was 0.93 and was significantly different from the 0.5 chance level (two-tailed sign test: p = 0.004). This result replicated our previous findings 22 , 28 .

Figure 5 ( a ) Mean ratio of responses for each subject in the baseline condition corresponding to the between hands transfer hypothesis (Fig.

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“…The perceived orientation of the triangle resulted from the expansions or contractions of the tactile bar combined with the movements of the hand. In a subsequent study we showed that this type of information transfer generalised to different limbs 28 .

Figure 2 ( a ) Truth table of triangle orientations corresponds to the integration between one movement and one tactile stimulus in the baseline condition (between hands transfer).

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Motion direction, luminance contrast, and speed perception: An unexpected meeting

“…In Experiment 4, the speed discrimination task was randomly alternated with a secondary control task similar to the one used by Dupin, Hayward, and Wexler (2017), to ensure that participants maintained the fixation on the central cross. The control task involved Landolt-like stimuli, consisting in a gray square with either the left or the right side missing (Michelson contrast: 17%).…”

Dynamic Displacement Vector Interacts with Tactile Localization

“…Any body movement produces concomitant cutaneous sensations, so movement and tactile stimulation are inextricably linked [ 12 , 13 ]. However, it remains unclear whether and how movement information affects tactile perception on body parts that do not move.…”

“…Importantly, relative localization of nearby tactile stimuli should be unaffected by such transformations. However, the spatial transformation may differ between two successive tactile stimulations because of the automatic integration of a concurrent displacement vector, even when the displacement is irrelevant and spatially remote [ 13 , 23 ]. In our case, the two successive tactile stimuli would use different remapping transformations, producing biases even in relative localization judgement.…”