Tool-use Actions Research Articles

Shaping multisensory action–space with tools: evidence from patients with cross-modal extinction

Recent findings from neurophysiology, neuropsychology and psychology have shown that peri-personal space is represented through an integrated multisensory processing. In humans, the interaction between peri-personal space representation and action execution can be revealed through the use of tools that, by extending the reachable space, modify the strength of visual–tactile extinction. We have previously shown that the peri-hand space whereby vision and touch are integrated can be expanded, and contracted, depending upon tool-use. Here, we show that these dynamic changes critically depend upon active tool-use, as they are not found after an equally long, but passive exposure to an elongated (hand + tool) body configuration. We also show that the extent of the peri-hand space elongation, as assessed at fixed far location (60 cm from the hand), varies according to the tool length such that a 30 cm long tool produced less elongation than a 60 cm long tool. This reveals for the first time that the distal border of elongated area is not sharply limited to the tool length, but extends beyond its physical size to include a peri-tool space whereby the strength of visual–tactile integration seems to fade. Remarkably, a similar amount of peri-hand space elongation was found when the effects of using a 30 cm long tool were compared with those produced by using a tool that was physically 60 cm long, but operationally 30 cm long. By dissociating with this ‘hybrid’ tool, the amount of space that is globally added to the hand (60 cm) from the one that is actually reachable (30 cm), we provide here the first evidence that the extent of peri-hand space elongation after tool use is tightly related to the functionally effective length of the tool, and not merely to its absolute length.

Gestural imitation and limb apraxia in corticobasal degeneration

Limb apraxia is a common symptom of corticobasal degeneration (CBD). While previous research has shown that individuals with CBD have difficulty imitating transitive (tool-use actions) and intransitive non-representational gestures (nonsense actions), intransitive representational gestures (actions without a tool) have not been examined. In the current study, eight individuals with CBD and eight age-matched healthy adults performed transitive, intransitive representational and intransitive non-representational gestures to imitation. The results indicated that compared to controls, individuals with CBD were significantly less accurate in the imitation of transitive and intransitive non-representational gestures but showed no deficits for the imitation of intransitive representational gestures. This advantage for intransitive representational gestures was thought to be due to fewer demands being placed on the analysis of visual-gestural information or the translation of this information into movement when imitating these gestures. These findings speak to the importance of context and the representation of gestures in memory in gesture performance.

Active tool use with the contralesional hand can reduce cross-modal extinction of touch on that hand

Active tool use with the contralesional hand can reduce cross-modal extinction of touch on that hand

Active Tool Use with the Contralesional Hand Can Reduce Cross-modal Extinction of Touch on that Hand

After a unilateral brain lesion, patients may show cross-modal, visual-tactile extinction. Such patients may fail to report tactile stimuli on the contralesional hand when presented together with competing visual stimuli near the ipsilesional hand. In this work we tested the hypothesis that this cross-modal extinction may be reduced when a patient has used a tool with the contralesional hand to reach for objects in the ipsilesional visual field. Consistent with previous work, we hypothesize that active use of a tool may extend cross-modal interactions between visual stimuli at the tip of the tool and tactile stimuli on the hand wielding the tool. In the new situation of a tool connecting the contralesional hand with ipsilesional visual space, competition between stimuli on these opposite sides may be reduced, so that extinction decreases. We studied patient BV, who showed reliable cross-modal, visual-tactile extinction after right-hemisphere stroke. In two separate sessions we showed that prolonged tool use (10-20 min) with the contralesional hand in ipsilesional space reduced cross-modal extinction for up to 60-90 min post-training. We propose that an actively used tool may be effective in linking cross-modal stimuli presented along its extension. This can then overcome competition between stimuli presented on opposite sides of the body midline, thus modulating extinction.

Active Tool Use with the Contralesional Hand Can Reduce Cross-modal Extinction of Touch on that Hand

Active Tool Use with the Contralesional Hand Can Reduce Cross-modal Extinction of Touch on that Hand

Tool-use changes multimodal spatial interactions between vision and touch in normal humans

In a visual–tactile interference paradigm, subjects judged whether tactile vibrations arose on a finger or thumb (upper vs. lower locations), while ignoring distant visual distractor lights that also appeared in upper or lower locations. Incongruent visual distractors (e.g. a lower light combined with upper touch) disrupt such tactile judgements, particularly when appearing near the tactile stimulus (e.g. on the same side of space as the stimulated hand). Here we show that actively wielding tools can change this pattern of crossmodal interference. When such tools were held in crossed positions (connecting the left hand to the right visual field, and vice-versa), the spatial constraints on crossmodal interference reversed, so that visual distractors in the other visual field now disrupted tactile judgements most for a particular hand. This phenomenon depended on active tool-use, developing with increased experience in using the tool. We relate these results to recent physiological and neuropsychological findings.