Abstract
To further elucidate the mechanisms underlying multisensory integration, this study examines the controversial issue of whether congruent inputs from three different sensory sources can enhance the perception of hand movement. Illusory sensations of clockwise rotations of the right hand were induced by either separately or simultaneously stimulating visual, tactile and muscle proprioceptive channels at various intensity levels. For this purpose, mechanical vibrations were applied to the pollicis longus muscle group in the subjects’ wrists, and a textured disk was rotated under the palmar skin of the subjects’ right hands while a background visual scene was projected onto the rotating disk. The elicited kinaesthetic illusions were copied by the subjects in real time and the EMG activity in the adductor and abductor wrist muscles was recorded. The results show that the velocity of the perceived movements and the amplitude of the corresponding motor responses were modulated by the nature and intensity of the stimulation. Combining two sensory modalities resulted in faster movement illusions, except for the case of visuo-tactile co-stimulation. When a third sensory input was added to the bimodal combinations, the perceptual responses increased only when a muscle proprioceptive stimulation was added to a visuo-tactile combination. Otherwise, trisensory stimulation did not override bimodal conditions that already included a muscle proprioceptive stimulation. We confirmed that vision or touch alone can encode the kinematic parameters of hand movement, as is known for muscle proprioception. When these three sensory modalities are available, they contribute unequally to kinaesthesia. In addition to muscle proprioception, the complementary kinaesthetic content of visual or tactile inputs may optimize the velocity estimation of an on-going movement, whereas the redundant kinaesthetic content of the visual and tactile inputs may rather enhance the latency of the perception.
Highlights
The Sherrington classification [1], which divides the human senses into the proprioceptive, exteroceptive and interoceptive categories, has been largely revisited and questioned
The application of vibratory stimulation to the right pollicis longus muscle, rotation of the tactile disk in a counterclockwise direction or the projection of a counterclockwise rotating visual pattern under the subjects’ hands induced an illusory sensation of clockwise rotation of the right hand in all of the subjects. This kinaesthetic illusion was accompanied by a slight involuntary motor response in the extensor carpi ulnaris (ECU) muscle of the subjects’ right wrists
No changes occurred in the pollicis longus (PL) muscle activity (Fig. 2)
Summary
The Sherrington classification [1], which divides the human senses into the proprioceptive, exteroceptive and interoceptive categories, has been largely revisited and questioned. An extensive body of data has shown that the sensory modalities characterised as exteroceptive contribute to the perception and control of human movement. Vision, which is classically described as an exteroceptive sense, has been found to play a proprioceptive role [2] especially based on the ‘‘vection’’ phenomenon studied during the 1970s [3,4]. By using microneurographic [5,6,7] and psychophysical methods [8,9,10,11], several groups have provided neurophysiological and behavioural data supporting the idea that touch plays a role in proprioceptive functions. It has been shown that cutaneous afferents from the skin that cover the dorsal part of the ankle [7], the knee [9], the fingers [8,11], the dorsum [5,6] and the palm of the hand [10] contribute to the detection and encoding of the kinematic parameters of imposed movements of these joints
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