Spatial constancy mechanisms in motor control

Abstract

The success of the human species in interacting with the environment depends on the ability to maintain spatial stability despite the continuous changes in sensory and motor inputs owing to movements of eyes, head and body. In this paper, I will review recent advances in the understanding of how the brain deals with the dynamic flow of sensory and motor information in order to maintain spatial constancy of movement goals. The first part summarizes studies in the saccadic system, showing that spatial constancy is governed by a dynamic feed-forward process, by gaze-centred remapping of target representations in anticipation of and across eye movements. The subsequent sections relate to other oculomotor behaviour, such as eye -head gaze shifts, smooth pursuit and vergence eye movements, and their implications for feed-forward mechanisms for spatial constancy. Work that studied the geometric complexities in spatial constancy and saccadic guidance across head and body movements, distinguishing between self-generated and passively induced motion, indicates that both feed-forward and sensory feedback processing play a role in spatial updating of movement goals. The paper ends with a discussion of the behavioural mechanisms of spatial constancy for arm motor control and their physiological implications for the brain. Taken together, the emerging picture is that the brain computes an evolving representation of three-dimensional action space, whose internal metric is updated in a nonlinear way, by optimally integrating noisy and ambiguous afferent and efferent signals.

Visual stability

“…But what is new in Cavanagh et al's proposal is to challenge the entire idea of dynamic receptive fields by suggesting that attention moves but receptive fields stay fixed. It does seem difficult, initially, to reconcile their proposal with all of the research showing receptive field shifts (see reviews in [20,21,23]). Another departure in their proposal is the claim that attentional pointers represent only a spatial location (in retinal coordinates), not objects or their features.…”

“…The change in the spatial profile of the receptive fields of neurons around the time of saccades is called 'remapping' [20][21][22], since the spatial map of the receptive field is temporarily altered. The neurophysiological evidence for remapping is discussed in detail in several of the reviews in this theme issue [20,21,23]. A number of studies which explore the pattern of remapping neurons in the brain, including the proportion of neurons that show remapping in different brain regions and the potential pathways that underlie remapping, are beginning to shed light on this process.…”

“…There is also evidence, both from single-cell recording in primates and functional MRI (fMRI) in humans, for dynamic receptive fields in the visual system itself (see [20,23]). One possibility is that the well-established connection from the FEF to visual areas such as V4 [75,76] plays a role in predictive remapping of visual neurons.…”

Spatiotopic coding and remapping in humans

“…We (and many others) suggest that the reason for this is that the information integrated from one fixation to the next is information about features-such as motion and form-not light elements or pixels. As other reviews in this issue point out [16][17][18][19][20][21], the process is not like 'sticking postage stamps on a tailor's dummy', integrating detailed 'snapshots' within a trans-saccadic buffer with an external metric. This would suggest that very early stages of analysis, such as V1, should not be spatiotopic, while higher centres responsible for motion and form (including middle temporal (MT) and medial superior temporal (MST) areas) might be spatiotopic.…”

Detecting peripersonal space: The promising role of ultrasonics

“…Such wide CBF modulations are in keeping with previous works indicating the activation of frontoparietal networks where the integration of sensory feedforward and feedback signals (including tactile, visual, and auditory stimuli provided near the body) related to the motor task demand and the surrounding environment occurs (Bremmer et al., 2001; Duhamel, Bremmer, Ben Hamed, & Graf, 1997; Graziano & Cooke, 2006; Graziano, Yap, & Gross, 1994; Gritsenko, Yakovenko, & Kalaska, 2009; Makin et al., 2007; Medendorp, 2011; Rizzolatti et al., 1981; Serino, Canzoneri, & Avenanti, 2011). These networks are functionally separated from that controlling the extrapersonal space, as suggested by control experiment (ii) results.…”