Catálogo de publicaciones - libros

In this chapter I discuss some of what can and cannot be visually perceived without spatial awareness, how attentional selection of visual information is affected by damage to neural systems that support spatial processing, how spatial processing in turn is involved in binding surface features such as color and shape together and how multiple spatial maps may guide attention. Relevance of neurolopsychological patient studies is also examined.

As organisms that move freely in space, we are adept at visually recognising objects regardless of their orientations. This facility probably does not depend on a “correction” mechanism, such as mental rotation, that might render an object in some canonical orientation. Rather, it is likely that an orientation-free description is extracted, probably by the ventral visual system. This suggests further that we can recognize the identity of an object before we can determine its orientation in space. This may depend in turn on the integration of shape information extracted by the ventral system with information about the space-occupying property of the object extracted by the dorsal system. The dissociation between identity and orientation may explain cases of “orientation agnosia,” in which the patient can recognize common objects but cannot determine their orientations. Orientation-free descriptions are nevertheless relatively crude. In order to distinguish between shapes that differ in more subtle ways, such as individual faces, or between shapes that are mirror-images of one another, a correction may be necessary, through either physical or mental rotation to the upright.

Mental rotation is an important part of human spatial cognition. In the last decade a growing number of brain imaging studies have been undertaken to uncover the neural underpinnings of mental rotation. These studies demonstrated that several brain areas are involved in the control of mental rotation. In this chapter we will summarize these. Although the reviewed studies differ in terms of used stimuli, mental rotation procedure, or brain imaging method, there is consistency for the core regions, which are involved in mental rotation (superior parietal lobe and the intraparietal sulcus). However, frontal, temporal, and occipital areas are also included into mental rotation processes depending on various aspects including used cognitive strategy, task difficulty, measuring protocol, or concentration of sexual hormones.

This chapter summarizes the spatial disorientation problems and navigation difficulties described by astronauts and cosmonauts, and relates them to research findings on orientation and navigation in humans and animals. Spacecraft crew are uniquely free to float in any relative orientation with respect to the cabin, and experience no vestibular and haptic cues that directly indicate the direction of “down”. They frequently traverse areas with inconsistently aligned visual vertical cues. As a result, most experience “Visual Reorientation Illusions” (VRIs) where the spacecraft floors, walls and ceiling surfaces exchange subjective identities. The illusion apparently results from a sudden reorientation of the observer’s allocentric reference frame. Normally this frame realigns to local interior surfaces, but in some cases it can jump to the Earth beyond, as with “Inversion Illusions” and EVA height vertigo. These perceptual illusions make it difficult for crew to maintain a veridical perception of orientation and place within the spacecraft, make them more reliant upon landmark and route strategies for 3D navigation, and can trigger space motion sickness. This chapter distinguishes VRIs and Inversion Illusions, based on firsthand descriptions from Vostok, Apollo, Skylab, Mir, Shuttle and International Space Station crew. Theories on human “gravireceptor” and “idiotropic” biases, visual “frame” and “polarity” cues, top-down processing effects on object orientation perception, mental rotation and “direction vertigo” are discussed and related to animal experiments on limbic head direction and place cell responses. It is argued that the exchange in perceived surface identity characteristic of human VRIs is caused by a reorientation of the unseen allocentric navigation plane used by CNS mechanisms coding place and direction, as evidenced in the animal models. Human VRI susceptibility continues even on long flights, perhaps because our orientation and navigation mechanisms evolved to principally support 2D navigation.

Spatial orientation in animals or in men requires memory as an essential feature and may be considered as a complex manifestation emerging from multiple brain structures with the hippocampus at “the crossroad”. In this chapter, we present the underlying biological mechanisms of spatial behavior along a contextual and historical dimension, in an ethological perspective. We propose that study of spatial memory in mammals, and more precisely in laboratory rats, sheds some light on the development and evolution of episodic memory.

Self-orientation in space is based on multisensory interactions of visual, vestibular and somatosensory-proprioceptive signals. In this article, we analyze vestibular signal processing in terms of its capacity to provide inertial cues for self-orientation in space. We show that vestibular signals from both the otolith organs and the semicircular canals must be processed in a bootstrap-operation like manner in order to obtain true inertial head-in-space orientation.

To what extent can we claim nowadays that we understand sensorimotor control of human dynamic behavior in space? We try here to answer this question by exploring whether the available knowledge base suffices to build a hominoid robot such that its sensorimotor control functions mimic those of humans. It is, actually, our aim to build such a robot. We want to use it, in a systems approach, for simulations to better understand human sensorimotor control functions. We posit that a systems approach is necessary to deal with this complex non-linear control. We are especially interested in the sensory aspects of the control, the inter-sensory interactions (‘multisensory integration’ or sensor fusion) and the spatio-temporal coordination. Psychophysical work in our laboratory showed that the brain creates from sensory inputs internal estimates of the physical stimuli in the outside world (i.e., of the external constellation that caused a particular set of sensor stimuli). For example, the brain derives from vestibular and proprioceptive signals an estimate of body support surface motion. It then uses these estimates for sensorimotor feedback control (rather than the ‘raw’ sensory signals such as the vestibular signal). We hold that this internal reconstruction of the external physics is required for appropriate spatio-temporal coordination of the behavior. However, a problem arises from non-ideal sensors. An example is the vestibular sensor, which shows pronounced low-frequency noise. The solution of this problem involves sensory re-weighting mechanisms. Based on the discovered sensor fusion principles, we built a hominoid robot for control of upright stance (which we consider a simple prototype of sensorimotor control). It mimics human stance control even in complex behavioral situations. We aim to use it to better understand sensorimotor deficits in neurological patients and to develop new therapy designs.

The aim of the present chapter is twofold. First it aims to show that perception requires action. This is most evident for space and action perception. Second, it aims to show that the distinction of the cortical visual processing into two streams is insufficient and leads to possible misunderstandings on the true nature of perceptual processes. I review empirical findings suggesting that visual processing is carried out along three distinct visual pathways qualified as dorso-dorsal, ventro-dorsal, and ventral streams. The relevant anatomical and functional features of the ventro-dorsal stream are presented and discussed.

We use mental imagery not only to anticipate future perception but also for our own movements. In this chapter we review the most recent literature in the domain of motor imagery, with particular emphasis on clinical findings. A wealth of evidence suggests that imagined movements of body parts draw - at least partly - on mechanisms associated with actual execution of the same movements. It is thus also possible to improve one’s motor performance via mental imagery techniques; motor imagery is widely used for athletes and researchers began to study its beneficial effects during rehabilitation in patients after cerebral lesions. Moreover, motor imagery is not restricted to single parts of the body. The body as whole can be rotated in imagery, for example, when we need to make a spatial judgment from another (or someone else’s) perspective. To better understand the mechanisms underlying whole body rotations in imagery we suggest investigating more specifically the yet rather neglected vestibular cortical projections, and discuss their possible role in cognitive tasks. We present an applied example showing how motor imagery training can change perception of movement.

A large proportion of right-brain damaged patients show unilateral neglect, a neurological deficit of perception, attention, representation, and/or performing actions within their left-sided space. The intriguing symptom is a spontaneous orientation bias toward the right leading to neglect of objects or persons on the left. This ipsilesional behaviour orientation bias may also affect the representational space. This particular aspect of neglect was seen as a failure to generate or maintain a normal representation of the left side of the mental image. Affected mental images can be of spatial or numerical nature. Representational neglect represents a cognitive disorder reflecting the selective damage of structures located in the right hemisphere and involved in spatial cognition. Surprisingly, these cognitive deficits may be positively modulated by passive physiological stimulation as caloric vestibular stimulation or stimulation of sensorimotor plasticity by prism adaptation procedure. These findings suggest that using low-level sensorimotor transformation may act on higher cognitive levels of space representation and consciousness according a bottom-up track.