Estimating the spatial Nyquist of the human EEG

The discrete sampling of the brain’s electrical field at the scalp surface with individual recording sensors is subject to the same sampling error as the discrete sampling of the time series at any one sensor with analog-to-digital conversion. Unlike temporal sampling, spatial sampling is intrinsically discrete, so that the post hoc application of analog anti-aliasing filters is not possible. However, the skull acts as a low-pass spatial filter of the brain’s electrical field, attenuating the high spatial frequency information. Because of the skull’s spatial filtering, a discrete sampling of the spatial field with a reasonable number of scalp electrodes is possible. In this paper, we provide theoretical and experimental evidence that adequately sampling the human electroencephalograph (EEG) across the full surface of the head requires a minimum of 128 sensors. Further studies with each of the major EEG and event-related potential phenomena are required in order to determine the spatial frequency of these phenomena and in order to determine whether additional increases in sensor density beyond 128 channels will improve the spatial resolution of the scalp EEG.     

The 36th Sir Frederick Bartlett Lecture: An associative analysis of spatial learning

The ability of animals to find important goals in their environment has been said to require a form of learning that is qualitatively different from that normally studied in the conditioning laboratory. Such spatial learning has been said to depend upon the construction of a global representation of the environment, and the acquisition of knowledge about the position of goals with reference to this representation is said to be unaffected by the presence of other cues or landmarks. To evaluate the first of these claims, experiments are described that investigated the extent to which the effects of training in one environment transfer to another. To evaluate the second claim, experiments are described that investigated whether cue competition effects normally found in conditioning studies can be found in spatial tasks. Overall, the results indicate that most of the phenomena of spatial learning can be explained by the principles of associative learning. The implications of the reported results for an understanding of the neural mechanisms of spatial learning are considered.     

Effects of phosphor persistence on perception and the control of eye movements

When a rapid eye movement (saccade) is made across material displayed on cathode ray tube monitors with short-persistence phosphors, various perceptual phenomena occur. The phenomena do not occur when the monitor has a long-persistence phosphor. These phenomena were observed for certain spatial arrays, their possible physiological basis noted, and their effect on the control of eye movements examined. When the display consisted simply of two dots, and a saccade was made from one to the other, a transient ghost image was seen just beyond the destination target. When the display consisted of vertical lines, tilting and displacement of the lines occurred. The phenomena were more intrusive for the latter display and there was a significant increase in the number of corrective saccades. These results are interpreted in terms of the effects of fluctuating illumination (and hence phosphor persistence) on saccadic suppression.     

The use of computer-controlled video disks in the study of spatial learning

The empirical study of spatial learning has been constrained by a range of methodological and technical limitations. Part of these are due to constraints in the stimulus delivery systems for pictorial displays that are available to the researcher. Surrogate travel systems—based on model photography, off-line computer graphics, and on-line computer graphics—provide alternative research settings. Yet none of the systems provides for both detailed displays and ease of subject interaction, both of which prove important in the investigation of spatial learning. Computer-controlled video-disk systems do allow both detail and interaction, therefore providing a research tool in which spatial learning phenomena can be observed carefully. A pilot study of spatial learning using a video-disk system is briefly described to demonstrate the sorts of phenomena observable with such a system.     

Spatial distortion induced by imperceptible visual stimuli

Previous studies have explored the effects of attention on spatial representation. Specifically, in the attentional repulsion effect, a transient visual cue that captures attention has been shown to alter the perceived position of a target stimulus to the direction away from the cue. The effect is also susceptible to retrospective influence, that attention appears to attract the target when the cue appears afterwards. This study examined the necessity of visual awareness of the cue in these phenomena. We found that when the cues were rendered invisible by backward visual masks, both repulsion and attraction effects were weakened but still observed. The results suggest that the effects possibly depend on processes that are not necessarily associated with conscious visual awareness of the cues. We conjecture that attentional shift produced by the weak, invisible cues may play a role in spatial distortion; but other possible accounts including non-attentional ones are also discussed.     

A simple neural network model of the hippocampus suggesting its pathfinding role in episodic memory retrieval

The goal of this work is to extend the theoretical understanding of the relationship between hippocampal spatial and memory functions to the level of neurophysiological mechanisms underlying spatial navigation and episodic memory retrieval. The proposed unifying theory describes both phenomena within a unique framework, as based on one and the same pathfinding function of the hippocampus. We propose a mechanism of reconstruction of the context of experience involving a search for a nearly shortest path in the space of remembered contexts. To analyze this concept in detail, we define a simple connectionist model consistent with available rodent and human neurophysiological data. Numerical study of the model begins with the spatial domain as a simple analogy for more complex phenomena. It is demonstrated how a nearly shortest path is quickly found in a familiar environment. We prove numerically that associative learning during sharp waves can account for the necessary properties of hippocampal place cells. Computational study of the model is extended to other cognitive paradigms, with the main focus on episodic memory retrieval. We show that the ability to find a correct path may be vital for successful retrieval. The model robustly exhibits the pathfinding capacity within a wide range of several factors, including its memory load (up to 30,000 abstract contexts), the number of episodes that become associated with potential target contexts, and the level of dynamical noise. We offer several testable critical predictions in both spatial and memory domains to validate the theory. Our results suggest that (1) the pathfinding function of the hippocampus, in addition to its associative and memory indexing functions, may be vital for retrieval of certain episodic memories, and (2) the hippocampal spatial navigation function could be a precursor of its memory function.     

No commonality between attentional capture and attentional blink

Visual search for a unique target is impaired when a salient distractor is presented (attentional capture). This phenomenon is said to occur because attention is diverted to a distractor before it reaches the target. Similarly, perception of the second of two targets embedded in a rapid stream of nontargets is impaired, suggesting attentional deprivation due to the processing of the first target (attentional blink). We examined whether these phenomena emerge from a common underlying attentional mechanism by using correlation studies. If these phenomena share a common foundation, the magnitude of these deficits should show within-subject correlations. Participants (N = 135) revealed significant attentional deficits during spatial and temporal capture and the attentional blink tasks. However, no significant correlation was found among these tasks. Experiment 2 (N = 95) replicated this finding using the same procedure as that used in Experiment 1 but included another attentional blink task that required spatial switching between the two targets. Strong correlations emerged only between the two attentional blink tasks (with/without spatial switching). The present results suggest that attentional deficits during spatial and temporal capture and the attentional blink tasks reflect different aspects of attention.     

Gaining perspective on spatial perspective taking

Spatial perspective taking is a term that encompasses a class of phenomena that assess the extent to which a perceiver can access spatial information relative to a viewpoint different from the perceiver’s egocentric viewpoint (e.g. something on my right is on the left of someone facing me). We investigated whether spatial perspective taking that involves judging how objects are oriented around an agent is susceptible to alterations in social motivations. In all experiments, participants saw a picture of two objects and asked to judge the relationship between the objects when there was, or was not, an agent between them. Results from Experiment 1 showed that participants spontaneously described the objects from the agent’s perspective when he was present. Experiments 2 and 3 explored whether this effect was altered by prior participant exposure to manipulations of social inclusion or social exclusion. Results from these two studies demonstrated that socially included participants and socially excluded participants did not differ in their tendencies to adopt the spatial perspective of another. These results are discussed in the context of the results of other studies showing that perspective taking can be influenced by social motivations.     

Object tracking and search in infancy: A review of data and a theoretical evaluation

Most research on infants' development of object and spatial concepts is based on object search tasks or visual tracking studies. In this review, it is concluded that many phenomena, particularly the tracking data, can be accounted for in terms of objective spatial perception in early infancy. However, some phenomena, particularly the stage IV search error, cannot be explained in these terms. A theoretical framework is put forward that integrates aspects of theory of direct perception with constructionist theory. First, it is proposed that objective properties of the basic spatial array are directly perceived, but that because perception is derived from action in the environment, there are initial limits to the scope and coherence of perception that diminish as the infant gains effective motor control. Second, it is proposed that in attempts to decipher the structure of social interchanges over objects, infants construct functional categorizations of objects that allow them to overcome limited awareness of their physical properties. Finally, it is suggested that these functional concepts provide an adequate means of interpreting the world, so that concepts based on the physical properties of objects, including their permanence, are relatively late developments.     

No commonality between attentional capture and attentional blink

Visual search for a unique target is impaired when a salient distractor is presented (attentional capture). This phenomenon is said to occur because attention is diverted to a distractor before it reaches the target. Similarly, perception of the second of two targets embedded in a rapid stream of nontargets is impaired, suggesting attentional deprivation due to the processing of the first target (attentional blink). We examined whether these phenomena emerge from a common underlying attentional mechanism by using correlation studies. If these phenomena share a common foundation, the magnitude of these deficits should show within-subject correlations. Participants (N?=?135) revealed significant attentional deficits during spatial and temporal capture and the attentional blink tasks. However, no significant correlation was found among these tasks. Experiment 2 (N?=?95) replicated this finding using the same procedure as that used in Experiment 1 but included another attentional blink task that required spatial switching between the two targets. Strong correlations emerged only between the two attentional blink tasks (with/without spatial switching). The present results suggest that attentional deficits during spatial and temporal capture and the attentional blink tasks reflect different aspects of attention.     

时空干扰效应：基于贝叶斯模型的解释

时空干扰效应是指时间知觉受空间信息干扰或空间知觉受时间信息干扰而出现错觉的现象。部分研究认为时空干扰是不对称的,空间对时间的干扰总是更大;还有研究认为时间和空间相互干扰的强度受实验因素影响,一般来说,空间对时间的干扰更大,但时间也能对空间产生同等程度甚至更大的干扰。在回顾隐喻理论和量值理论的主要观点之后,重点分析贝叶斯模型对时空干扰效应的解释,最后提出未来研究应关注的三个问题,即拓展贝叶斯模型对时空干扰效应的解释范围,探明基于贝叶斯推断的时空干扰神经机制和探索时空干扰的调控方法。     

The role of location indexes in spatial perception: a sketch of the FINST spatial-index model

This paper hypothesizes a resource-limited mechanism, called a FINST, for individuating or indexing visual features, as distinct from encoding their type or location. FINSTs have the property that they index features in a way that is transparent to their retinal location, and hence under certain conditions succeed in "pointing to" scene locations. The basic assumption is that no operation upon sets of features can occur unless all the features to which the operation applies are first FINSTed. A number of applications of this hypothesis are explored in this paper, including applications to phenomena such as the spatial stability of visual percepts, the ability to track several independently moving targets in parallel, the ability to detect a class of spatial relations requiring the use of "visual routines", various mental imagery phenomena, and the ability to encode complex shapes for recognition. In addition, the possibility is examined that such indexes might be used to bind perceived locations to arguments in motor commands, thereby allowing some forms of perceptual-motor coordination. Several additional assumptions are introduced for this purpose, including the postulation of other indexes (called ANCHORS) for non-visually sensed locations. It is assumed that ANCHORS can be bound to FINSTs, thus allowing cross-referencing of visually detected locations to locations given within a proprioceptive or motor-command frame of reference.     

Attention and the crossmodal construction of space

Traditional studies of spatial attention consider only a single sensory modality at a time (e.g. just vision, or just audition). In daily life, however, our spatial attention often has to be coordinated across several modalities. This is a non-trivial problem, given that each modality initially codes space in entirely different ways. In the last five years, there has been a spate of studies on crossmodal attention. These have demonstrated numerous crossmodal links in spatial attention, such that attending to a particular location in one modality tends to produce corresponding shifts of attention in other modalities. The spatial coordinates of these crossmodal links illustrate that the internal representation of external space depends on extensive crossmodal integration. Recent neuroscience studies are discussed that suggest possible brain mechanisms for the crossmodal links in spatial attention.     

A qualitative analysis of sensory phenomena induced by perceptual deprivation

Previous studies have shown that misperceptions and illusory experiences can occur if sensory stimulation is withdrawn or becomes invariant even for short periods of time. Using a perceptual deprivation paradigm, we created a monotonous audiovisual environment and asked participants to verbally report any auditory, visual or body-related phenomena they experienced. The data (analysed using a variant of interpretative phenomenological analysis) revealed two main themes: (1) reported sensory phenomena have different spatial characteristics ranging from simple percepts to the feeling of immersion in a complex multisensory environment and (2) the active contribution of the perceiver where participants report engaging in exploratory processes even when there is nothing to find. Detailed analysis of the qualitative data further showed that participants who reported more perceptual phenomena were more likely to report internal bodily sensations, move more during the experiment and score higher on the Revised Hallucination Scale than those reporting fewer percepts explicitly linking perceptual deprivation to somatic phenomena. The results demonstrate how the variety of sensory experiences induced by perceptual deprivation can give further insight into the factors mediating conscious awareness and may suggest ways in which the brain imposes meaning on the environment under invariant sensory conditions.     

When do spatial abilities support student comprehension of STEM visualizations?

Spatial visualization abilities are positively related to performance on science, technology, engineering, and math tasks, but this relationship is influenced by task demands and learner strategies. In two studies, we illustrate these interactions by demonstrating situations in which greater spatial ability leads to problematic performance. In Study 1, chemistry students observed and explained sets of simultaneously presented displays depicting chemical phenomena at macroscopic and particulate levels of representation. Prior to viewing, the students were asked to make predictions at the macroscopic level. Eye movement analyses revealed that greater spatial ability was associated with greater focus on the prediction-relevant macroscopic level. Unfortunately, that restricted focus was also associated with lower-quality explanations of the phenomena. In Study 2, we presented the same displays but manipulated whether participants were asked to make predictions prior to viewing. Spatial ability was again associated with restricted focus, but only for students who completed the prediction task. Eliminating the prediction task encouraged attempts to integrate the displays that related positively to performance, especially for participants with high spatial ability. Spatial abilities can be recruited in effective or ineffective ways depending on alignments between the demands of a task and the approaches individuals adopt for completing that task.     

Directional harmonic theory: a computational Gestalt model to account for illusory contour and vertex formation

Visual illusions and perceptual grouping phenomena offer an invaluable tool for probing the computational mechanism of low-level visual processing. Some illusions, like the Kanizsa figure, reveal illusory contours that form edges collinear with the inducing stimulus. This kind of illusory contour has been modeled by neural network models by way of cells equipped with elongated spatial receptive fields designed to detect and complete the collinear alignment. There are, however, other illusory groupings which are not so easy to account for in neural network terms. The Ehrenstein illusion exhibits an illusory contour that forms a contour orthogonal to the stimulus instead of collinear with it. Other perceptual grouping effects reveal illusory contours that exhibit a sharp corner or vertex, and still others take the form of vertices defined by the intersection of three, four, or more illusory contours that meet at a point. A direct extension of the collinear completion models to account for these phenomena tends towards a combinatorial explosion, because it would suggest cells with specialized receptive fields configured to perform each of those completion types, each of which would have to be replicated at every location and every orientation across the visual field. These phenomena therefore challenge the adequacy of the neural network approach to account for these diverse perceptual phenomena. I have proposed elsewhere an alternative paradigm of neurocomputation in the harmonic resonance theory (Lehar 1999, see website), whereby pattern recognition and completion are performed by spatial standing waves across the neural substrate. The standing waves perform a computational function analogous to that of the spatial receptive fields of the neural network approach, except that, unlike that paradigm, a single resonance mechanism performs a function equivalent to a whole array of spatial receptive fields of different spatial configurations and of different orientations, and thereby avoids the combinatorial explosion inherent in the older paradigm. The present paper presents the directional harmonic model, a more specific development of the harmonic resonance theory, designed to account for specific perceptual grouping phenomena. Computer simulations of the directional harmonic model show that it can account for collinear contours as observed in the Kanizsa figure, orthogonal contours as seen in the Ehrenstein illusion, and a number of illusory vertex percepts composed of two, three, or more illusory contours that meet in a variety of configurations.     

What clocks tell us about the neural correlates of spatial imagery

We review a series of experimental studies aimed at answering some critical questions about the neural basis of spatial imagery. Our group used functional magnetic resonance imaging (fMRI) to explore the neural correlates of an online behaviourally controlled spatial imagery task without need for visual presentation—the mental clock task. Subjects are asked to imagine pairs of times that are presented acoustically and to judge at which of the two times the clock hands form the greater angle. The cortical activation elicited by this task was contrasted with that obtained during other visual, perceptual, verbal, and spatial imagery tasks in several block design studies. Moreover, our group performed an event‐related fMRI study on the clock task to investigate the representation of component cognitive processes in spatial imagery. The bulk of our findings demonstrates that cortical areas in the posterior parietal cortex (PPC), along the intraparietal sulcus, are robustly involved in spatial mental imagery and in other tasks requiring spatial transformations. PPC is bilaterally involved in different kinds of spatial judgement. Yet the degree to which right and left PPC are activated in different tasks is a function of task requirements. From event‐related fMRI data we obtained evidence that left and right PPC are activated asynchronously during the clock task and this could reflect their different functional role in subserving cognitive components of visuospatial imagery.     

Parallel patterns of spatial compatibility and spatial congruence…as long as you don't look too closely

The effects of spatial compatibility and spatial congruence have both been explained in terms of a dual-route model under which spatial information about the stimulus, regardless of task relevance, is directly passed from perception to action. Recently, however, some alternatives to the dual-route model of the Simon Effect have been proposed (or re-introduced) as viable explanations. The present experiment compared the magnitudes of the effects of spatial compatibility and spatial congruence across a range of tasks that varied in their dimensional overlap. The results exhibited a remarkable parallel between the two phenomena when viewed only in terms of the interaction between stimulus set and response set. This could be taken as new evidence for a common origin. However, when the entire pattern of results was examined, a large difference between compatibility and congruence were also seen, which implies that there is at least one important difference between the two phenomena.     

The cognitive and neural correlates of "tactile consciousness": a multisensory perspective

People's awareness of tactile stimuli has been investigated in far less detail than their awareness of stimuli in other sensory modalities. In an attempt to fill this gap, we provide an overview of studies that are pertinent to the topic of tactile consciousness. We discuss the results of research that has investigated phenomena such as "change blindness", phantom limb sensations, and numerosity judgments in tactile perception, together with the results obtained from the study of patients affected by deficits that can adversely affect tactile perception such as neglect, extinction, and numbsense. The similarities as well as some of the important differences that have emerged when visual and tactile conscious information processing have been compared using similar experimental procedures are highlighted. We suggest that conscious information processing in the tactile modality cannot be separated completely from the more general processing of spatial information in the brain. Finally, the importance of considering tactile consciousness within the larger framework of multisensory information processing is also discussed.