Abstract
Maintaining or modifying the speed and direction of locomotion requires the coupling of the locomotion with the retinal optic flow that it generates. It is shown that this essential behavioral capability, which requires on-line neural control, is preserved in the cortically blind hemifield of a hemianope. In experiments, optic flow stimuli were presented to either the normal or blind hemifield while the patient was walking on a treadmill. Little difference was found between the hemifields with respect to the coupling (i.e. co-dependency) of optic flow detection with locomotion. Even in the cortically blind hemifield, faster walking resulted in the perceptual slowing of detected optic flow, and self-selected locomotion speeds demonstrated behavioral discrimination between different optic flow speeds. The results indicate that the processing of optic flow, and thereby on-line visuo-locomotor coupling, can take place along neural pathways that function without processing in Area V1, and thus in the absence of conscious intervention. These and earlier findings suggest that optic flow and object motion are processed in parallel along with correlated non-visual locomotion signals. Extrastriate interactions may be responsible for discounting the optical effects of locomotion on the perceived direction of object motion, and maintaining visually guided self-motion.
Highlights
The relationship between perception and action has been of long-standing interest to researchers concerned with both visual processing and motor control
Visuo-locomotor coupling occurs while walking on a treadmill, where it takes the form of locomotion-induced slowing of perceived optic flow speed (Experiment 1), and on matching walking speed to constant or changing optic flow speed (Experiments 2 and 3)
The results of the current study show that during visuo-locomotor coupling neither the slowing effect nor speed matching requires processing in the geniculostriate pathways that sustain conscious awareness of visual stimuli
Summary
The relationship between perception and action has been of long-standing interest to researchers concerned with both visual processing and motor control Indicative of their co-dependence is evidence that locomotion can induce changes in the perceived speed of concurrent optic flow (Pelah & Barlow, 1996; Thurrell, Pelah & Distler, 1998; Thurrell & Pelah, 2002, 2005; Durgin, Gigone & Scott, 2005), that changes in optic flow speed while walking at a constant speed can signal an impending collision (Lee, 1980), and that locomotion can change involuntarily in response to changes in optic flow (Prokop, Schubert & Berger, 1997; Dong, Pelah, Cameron & Lasenby, 2008). A noteworthy feature of locomotion in normally sighted individuals is that retrospectively (and introspectively) episodes of walking seem to have taken place without conscious awareness or attention to the optic flow pattern that had been generated by the locomotion. The objective of this study is to determine whether behavior requiring the detection of optic flow and its inherent coupling with locomotion are preserved, despite the absence of processing in Area V1 and the accompanying loss of conscious awareness
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