Where you look can influence haptic object recognition

Applying a novel visual-to-touch sensory substitution for studying tactile reference frames

Perceiving the spatial location and physical dimensions of touched objects is crucial for goal-directed actions. To achieve this, our brain transforms skin-based coordinates into a reference frame by integrating visual and posture information. In the current study, we examine the role of posture in mapping tactile sensations to a visual image. We developed a new visual-to-touch sensory substitution device that transforms images into a sequence of vibrations on the arm. 52 blindfolded participants performed spatial recognition tasks in three different arm postures and had to switch postures between trial blocks. As participants were not told which side of the device is down and which is up, they could choose how to map its vertical axis in their responses. Contrary to previous findings, we show that new proprioceptive inputs can be overridden in mapping tactile sensations. We discuss the results within the context of the spatial task and the various sensory contributions to the process.

Long-term memory of haptic and visual information in older adults

The present study examined haptic and visual memory capacity for familiar objects through the application of an intentional free-recall task with three-time intervals in a sample of 78 healthy older adults without cognitive impairment. A wooden box and a turntable were used for the presentation of haptic and visual stimuli, respectively. The procedure consisted of two phases, a study phase that consisted of the presentation of stimuli, and a test phase (free-recall task) performed after one hour, one day or one week. The analysis of covariance (ANCOVA) indicated that there was a main effect only for the time intervals (F (2,71) = 12.511, p = .001, η² = 0.261), with a lower recall index for the interval of one week compared to the other intervals. We concluded that the memory capacity between the systems (haptic and visual) is similar for long retrieval intervals (hours to days).

Multisensory integration substantiates distributed and overlapping neural networks

The hypothesis that highly overlapping networks underlie brain functions (neural reuse) is decisively supported by three decades of multisensory research. Multisensory areas process information from more than one sensory modality and therefore represent the best examples of neural reuse. Recent evidence of multisensory processing in primary visual cortices further indicates that neural reuse is a basic feature of the brain.

Disentangling the External Reference Frames Relevant to Tactile Localization

Different reference frames appear to be relevant for tactile spatial coding. When participants give temporal order judgments (TOJ) of two tactile stimuli, one on each hand, performance declines when the hands are crossed. This effect is attributed to a conflict between anatomical and external location codes: hand crossing places the anatomically right hand into the left side of external space. However, hand crossing alone does not specify the anchor of the external reference frame, such as gaze, trunk, or the stimulated limb. Experiments that used explicit localization responses, such as pointing to tactile stimuli rather than crossing manipulations, have consistently implicated gaze-centered coding for touch. To test whether crossing effects can be explained by gaze-centered coding alone, participants made TOJ while the position of the hands was manipulated relative to gaze and trunk. The two hands either lay on different sides of space relative to gaze or trunk, or they both lay on one side of the respective space. In the latter posture, one hand was on its "regular side of space" despite hand crossing, thus reducing overall conflict between anatomical and external codes. TOJ crossing effects were significantly reduced when the hands were both located on the same side of space relative to gaze, indicating gaze-centered coding. Evidence for trunk-centered coding was tentative, with an effect in reaction time but not in accuracy. These results link paradigms that use explicit localization and TOJ, and corroborate the relevance of gaze-related coding for touch. Yet, gaze and trunk-centered coding did not account for the total size of crossing effects, suggesting that tactile localization relies on additional, possibly limb-centered, reference frames. Thus, tactile location appears to be estimated by integrating multiple anatomical and external reference frames.

Simultaneous Sketching Aids the Haptic Identification of Raised Line Drawings

Haptically identifying raised line drawings is difficult. We investigated whether a major component of this difficulty lies in acquiring, integrating, and maintaining shape information from touch. Wijntjes, van Lienen, Verstijnen, and Kappers reported that drawings which participants had failed to identify by touch alone could often subsequently be named if they were sketched. Thus, people sometimes needed to externalize haptically acquired information by making a sketch in order to be able to use it. We extended Wijntjes et al.'s task and found that sketching while touching improved drawing identification even more than sketching after touching, but only if people could see their sketches. Our results suggest that the slow, serial nature of information acquisition seriously hampers the haptic identification of raised line drawings relative to visually identifying line drawings. Simultaneous sketching may aid identification by reducing the burden on working memory and by helping to guide haptic exploration. This conclusion is consistent with the finding reported by Lawson and Bracken that 3-D objects are much easier to identify haptically than raised line drawings since, unlike for vision, simultaneously extracting global shape information is much easier haptically for 3-D stimuli than for line drawings.

The contributions of vision and haptics to reaching and grasping

This review aims to provide a comprehensive outlook on the sensory (visual and haptic) contributions to reaching and grasping. The focus is on studies in developing children, normal, and neuropsychological populations, and in sensory-deprived individuals. Studies have suggested a right-hand/left-hemisphere specialization for visually guided grasping and a left-hand/right-hemisphere specialization for haptically guided object recognition. This poses the interesting possibility that when vision is not available and grasping relies heavily on the haptic system, there is an advantage to use the left hand. We review the evidence for this possibility and dissect the unique contributions of the visual and haptic systems to grasping. We ultimately discuss how the integration of these two sensory modalities shape hand preference.