Kinesthetic perception of visually specified axes

Interaction between reference frames during subjective vertical estimates in a tilted immersive virtual environment

Numerous studies highlighted the influence of a tilted visual frame on the perception of the visual vertical ('rod-and-frame effect' or RFE). Here, we investigated whether this influence can be modified in a virtual immersive environment (CAVE-like) by the structure of the visual scene and by the adjustment mode allowing visual or visuo-kinaesthetic control (V and VK mode, respectively). The way this influence might dynamically evolve throughout the adjustment was also investigated in two groups of subjects with the head unrestrained or restrained upright. RFE observed in the immersive environment was qualitatively comparable to that obtained in a real display (portable rod-and-frame test; Oltman 1968, Perceptual and Motor Skills 26 503-506). Moreover, RFE in the immersive environment appeared significantly influenced by the structure of the visual scene and by the adjustment mode: the more geometrical and meaningful 3-D features the visual scene contained, the greater the RFE. The RFE was also greater when the subjective vertical was assessed under visual control only, as compared to visuo-kinaesthetic control. Furthermore, the results showed a significant RFE increase throughout the adjustment, indicating that the influence of the visual scene upon subjective vertical might dynamically evolve over time. The latter effect was more pronounced for structured visual scenes and under visuo-kinaesthetic control. On the other hand, no difference was observed between the two groups of subjects having the head restrained or unrestrained. These results are discussed in terms of dynamic combination between coexisting reference frames for spatial orientation.

Visual cortex activation in kinesthetic guidance of reaching

The purpose of this research was to determine the cortical circuit involved in encoding and controlling kinesthetically guided reaching movements. We used (15)O-butanol positron emission tomography in ten blindfolded able-bodied volunteers in a factorial experiment in which arm (left/right) used to encode target location and to reach back to the remembered location and hemispace of target location (left/right side of midsagittal plane) varied systematically. During encoding of a target the experimenter guided the hand to touch the index fingertip to an external target and then returned the hand to the start location. After a short delay the subject voluntarily moved the same hand back to the remembered target location. SPM99 analysis of the PET data contrasting left versus right hand reaching showed increased (P < 0.05, corrected) neural activity in the sensorimotor cortex, premotor cortex and posterior parietal lobule (PPL) contralateral to the moving hand. Additional neural activation was observed in prefrontal cortex and visual association areas of occipital and parietal lobes contralateral and ipsilateral to the reaching hand. There was no statistically significant effect of target location in left versus right hemispace nor was there an interaction of hand and hemispace effects. Structural equation modeling showed that parietal lobe visual association areas contributed to kinesthetic processing by both hands but occipital lobe visual areas contributed only during dominant hand kinesthetic processing. This visual processing may also involve visualization of kinesthetically guided target location and use of the same network employed to guide reaches to visual targets when reaching to kinesthetic targets. The present work clearly demonstrates a network for kinesthetic processing that includes higher visual processing areas in the PPL for both upper limbs and processing in occipital lobe visual areas for the dominant limb.