Abstract
Growing evidence indicates that perceptual-motor codes may be associated with and influenced by actual bodily states. Following a spinal cord injury (SCI), for example, individuals exhibit reduced visual sensitivity to biological motion. However, a dearth of direct evidence exists about whether profound alterations in sensorimotor traffic between the body and brain influence audio-motor representations. We tested 20 wheelchair-bound individuals with lower skeletal-level SCI who were unable to feel and move their lower limbs, but have retained upper limb function. In a two-choice, matching-to-sample auditory discrimination task, the participants were asked to determine which of two action sounds matched a sample action sound presented previously. We tested aural discrimination ability using sounds that arose from wheelchair, upper limb, lower limb, and animal actions. Our results indicate that an inability to move the lower limbs did not lead to impairment in the discrimination of lower limb-related action sounds in SCI patients. Importantly, patients with SCI discriminated wheelchair sounds more quickly than individuals with comparable auditory experience (i.e. physical therapists) and inexperienced, able-bodied subjects. Audio-motor associations appear to be modified and enhanced to incorporate external salient tools that now represent extensions of their body schemas.
Highlights
The notion of embodied cognition postulates that knowledge is grounded on actual bodily states and that higher-order processes, such as mind- and intention- reading or action- and perception- understanding, can be mapped onto modal sensorimotor cortices[1]
The post hoc comparisons revealed that the patients with spinal cord injury (SCI) discriminated the wheelchair-related action sounds (WRAS) earlier (652 msec) than the able-bodied individuals with comparable auditory experience and those with no comparable perceptual experience
In patients with SCI, the reaction times (RTs) for WRAS were comparable to the RTs elicited by upper (URAS = 703 msec, p > 0.26) but not of lower limb action sounds (LRAS = 760 msec, p < 0.02)
Summary
The notion of embodied cognition postulates that knowledge is grounded on actual bodily states and that higher-order processes, such as mind- and intention- reading or action- and perception- understanding, can be mapped onto modal sensorimotor cortices[1]. Direct action perception strengthens motor representation[9], and short-term motor experiences with a particular action may influence its visual recognition[10] and facilitate action prediction[11]. The mechanisms and neural structures involved in the motor coding of action-related sounds have been explored in able individuals using correlative and causative approaches[13,14,15,16,17,18]. These studies indicate that the perception of sounds from body part specific actions (e.g. ripping a sheet of paper) activates the left fronto-parietal network[19] in a somatotopic arrangement[16,20]. People with SCI who are paralyzed and wheelchair-bound could treat their relevant artificial tools (wheelchair) as an extension/substitution of the functionality of the affected body part[41]
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