A. H. C. van der Heijden

A THEORY OF VISUAL STABILITY ACROSS SACCADIC EYE MOVEMENTS

We identify two aspects of the problem of maintaining perceptual stability despite an observers eye movements. The first, visual direction constancy, is the (egocentric) stability of apparent positions of objects in the visual world relative to the perceiver. The second, visual position constancy, is the (exocentric) stability of positions of objects relative to each other. We analyze the constancy of visual direction despite saccadic eye movements. Three information sources have been proposed to enable the visual system to achieve stability: the structure of the visual field, proprioceptive inflow, and a copy of neural efference or outflow to the extraocular muscles. None of these sources by itself provides adequate information to achieve visual direction constancy; present evidence indicates that all three are used. Our final question concerns how information processing operations result in a stable world. The three traditionally suggested means have been elimination, translation, or evaluation. All are rejected. From a review of the physiological and psychological evidence we conclude that no subtraction, compensation, or evaluation need take place. The problem for which these solutions were developed turns out to be a false one. We propose a “calibration” solution: correct spatiotopic positions are calculated anew for each fixation. Inflow, outflow, and retinal sources are used in this calculation: saccadic suppression of displacement bridges the errors between these sources and the actual extent of movement.

SLAM: A connectionist model for attention in visual selection tasks

SLAM, the SeLective Attention Model, performs visual selective attention tasks, an analysis of which shows that two processes, object and attribute selection, are both necessary and sufficient. It is based upon the McClelland and Rumelhart (1981) model for visual word recognition, with the addition of a response selection and evaluation mechanism. The responses may be correct or incorrect and, in particular conditions, SLAM may not make a response at all. Moreover, it allows for the generation of specific responses in time. SLAMs main characteristics are parallelism restricted by competition within modules, heterarchical processing in a hierarchical structure, and generation of responses as a result of relaxation given the conjoint constraints of stimulation, object, and attribute selection. The model is considered to represent an individual subject performing filtering tasks and demonstrates appropriate selective behavior. It is also tested quantitatively using a single tentative set of model parameters. The study reports simulations of four different filtering experiments, modeling response latencies, and error proportions. Specifications are made to take account of instructions, previous trials, and the effect of a barmarker cue and of asynchronies in stimulus and cue onsets. The model is then extended in order to provide simulations of a number of Stroop experiments, which can be regarded as filtering tasks with nonequivalent stimuli. The extension required for Stroop simulations is the addition of direct connections between compatible stimulus and response aspects. The direct connections do not affect the simulation of simpler filtering tasks. A variety of different experiments carried out by different authors is simulated. The model is discussed in terms of how modular architecture and the interaction of excitation and inhibition generate facilitation or inhibition of response latencies.

Search for a conjunctively defined target can be selectively limited to a color-defined subset of elements.

Bij een conjunctietarget van kleur en orientatie zoeken proefpersonen alleen die elementen af die dezelfde kleur hebben als de target.

Visual selective attention: Introductory remarks

Theories of selective attention are often put forward as having, in intent, equivalent application to audition, to vision, and, for that matter, to information processing in all other sensory modalities. However, there are certain fundamental differences in the character of information processing in vision and audition; the wiser, or at least the more cautious strategy, may be to concentrate, first of all, on developing models of the selective processes within the different senses individually. Only then, when our understanding of selection within these functionally very different modalities is more secure, will it perhaps be fruitful to look for generalizations about the selection mechanisms across different sensory systems. Accordingly, this special issue is devoted exclusively to studies on selective attention in vision. The early ideas on selective attention, within the information-processing framework, were shaped principally by work on auditory selection, in particular by the demands of selection among concurrent speech signals. In part, this was due to the human engineering context in which modern research on attention evolved. However, there was also a widespread belief that hearing is, because of its functional properties, especially suited to the study of attentional selection. This was, for example, the main message in the introductory chapter of Broadbents (1958) influential monograph, the argument being that auditory selection is almost completely central, whereas peripheral sensory adjustments play a large part in visual selection. In the decades during which modern attention research took shape, theories of attention were thus essentially theories of auditory attention. When attention research began to be extended to the visual modality, many of the central ideas and theoretical alternatives had already been formulated, and theorizing continued to be influenced by them. Meanwhile as witnessed by the contributions to this special issue visual attention has come of age as a research field; it may be timely to consider its particular functional basis. One first step towards adequate theorizing about visual attention is to consider in which respects visual information processing is different from auditory information processing. The properties of vision that are potentially relevant to our understanding of visual attention, and that we

The information-processing approach

SummaryThe information-processing (IP) approach to perception and cognition arose as a reaction to behaviourism. This reaction mainly concerned the nature of explanation in scientific psychology. The “standard” account of behaviour, phrased in strictly external terms, was replaced by a “realist” account, phrased in terms of internal entities and processes. An analysis of the theoretical language used in IP psychology shows an undisciplined state of affairs. A great number of languages is simultaneously in use; no level of analysis is unambiguously referred to; and basic concepts such as information and processing remain largely undefined. Nevertheless, over the past 25 years the IP approach has developed into a disciplined and sophisticated experimental science. A look at actual practice hints at the basic reason for its success. The approach is not so much concerned with absolute or intrinsic properties of the human information processor, but with what can be called its relative or differential properties. A further analysis of this feature of the IP approach in terms of the formal language of a logical system makes explicit the basis of its success. The IP approach can be regarded as developing an empirical difference calculus on an unspecified class of objects, phrased in terms of a simulated “theory-neutral” observation language, and with operators that are structurally analogous to logical operators. This reinterpretation of what the IP approach is about brings a number of advantages. It strengthens its position as an independent science, clarifies its relation with other approaches within psychology and other sciences within the cognitive science group, and makes it independent of philosophical subtleties.

Relative mislocalization of briefly presented stimuli in the retinal periphery

We studied the ability to localize flashed stimuli, using a relative judgment task. When observers are asked to localize the peripheral position of a probe with respect to the midposition of a spatially extended comparison stimulus, they tend to judge the probe as being more toward the periphery than is the midposition of the comparison stimulus. We report seven experiments in which this novel phenomenon was explored. They reveal that the mislocalization occurs only when the probe and the comparison stimulus are presented in succession, independent of whether the probe or the comparison stimulus comes first (Experiment 1). The size of the mislocalization is dependent on the stimulus onset asynchrony (Experiment 2) and on the eccentricity of presentation (Experiment 3). In addition, the illusion also occurs in an absolute judgment task, which links mislocalization with the general tendency to judge peripherally presented stimuli as being more foveal than they actually are (Experiment 4). The last three experiments reveal that relative mislocalization is affected by the amount of spatial extension of the comparison stimulus (Experiment 5) and by its structure (Experiments 6 and 7). This pattern of results allows us to evaluate possible explanations of the illusion and to relate it to comparable tendencies observed in eye movement behavior. It is concluded that the system in charge of the guidance of saccadic eye movements is also the system that provides the metric in perceived visual space.

The role of position in object selection in vision

SummaryWithin contemporary visual-information-processing psychology, two classes of selective-attention theories can be distinguished: position-not-special theories and position-special theories. The position-not-special theories postulate that attentional selection by colour, by form, and by position are equivalent selective operations. The position-special theories assume that selection by position is more basic or direct than selection by colour or by form. Examples of both types of theory are briefly described, and irrelevant and relevant evidence is critically discussed. It is concluded that the relevant evidence is directly compatible with the position-special views and that the position-not-special theories require additional extraneous assumptions. The position-special model presented in Van der Heijden (1992) is elaborated in further detail. It is shown that this model is compatible with two important and often substantiated assumptions of the position-not-special theories: the assumption that pre-attentive analysers organize the visual scene in objects against a background, and the assumption that visual-selective attention can be directed at objects isolated in this way. This position-special theory is a parsimonious theory because it can identify the mentalistic conceptselective attention with the materialistic conceptspatial position.

Two stages in postcategorical filtering and selection

In a modified Stroop paradigm, Kahneman and Henik (1981) varied the spatial location of incompatible color words in relation to the position of the ink color to be named. A large effect on reaction time was found if the word was in the same position as the color, and a greatly reduced effect was found if it was in a different location. Kahneman and Henik concluded that (1) attention can be directed only to preattentively defined perceptual objects, (2) attention facilitates all the responses associated with properties or elements of the selected object, and (3) word reading is not automatic as proposed in unlimited capacity (UC) models. To evaluate these conclusions, the same paradigm was used in three experiments. The first two essentially replicated Kahneman and Henik’s findings and supported the first two conclusions. The third experiment tested the capacity issue. The results provided no reason for rejecting the UC assumption. A theoretical analysis is outlined showing how a UC processing model with an object-selection stage and a subsequent dimension-selection stage can account for the results obtained. This model is an extended version of Van der Heijden’s (1981) postcategorical filtering model.

Target-noise separation in visual selective attention.

Abstract Several studies have reported a decrease of interference caused by the categorical nature of noise stimuli, i.e., identity-dependent interference, with increasing physical target-noise separation. Such a result is generally regarded as evidence in favour of precategorical selection (‘beam-of-spot-light’) views of attention. Analysis of these studies, however, reveals that target-noise distance covaried with distance of the noise elements from the fixation point, that is, with retinal acuity. In this study, two experiments are reported in which identity-dependent interference in a colour-naming task (the ‘Stroop effect’) was investigated as a function of colour-noise separation. All stimulus elements were projected on positions of equal retinal acuity. No effect of target-noise separation was observed. The results are interpreted as evidence in favour of postcategorical-selection views; selective attention deals with identified information and has its function in the programming and execution of further actions like memory storage and overt responding.

The effects of advance location cueing on latencies in a single-letter recognition task

SummaryThis study investigates facilitating effects of foreknowledge of position in single-letter recognition tasks with latency as the dependent variable. Three kinds of cue are used: symbolic cues, location cues and neutral cues. For the effects of symbolic and location cues the following predictions are derived from the literature: increasing benefits with increasing SOAs for symbolic cues and constant benefits with increasing SOAs for location cues.Cue-detection times and letter-recognition times with the different cues were determined in three experiments. In the experiments the same general paradigm was used. In Experiment 1 cue-detection times appeared to differ as a function of cue eccentricity; in Experiments 2 and 3 cues were adjusted in such a way that cue-detection times were about the same. Cues reliably indicated the target position in Experiments 1 and 2; in Experiment 3 cue validity was reduced to 50%.The cueing results conformed partly to the predictions. All experiments suggested a small benefit under symbolic cueing and a larger benefit under location cueing. Except for the smallest SOA used, for both types of cue benefits were invariant over SOAs. The implications of these results in relation to other single-letter recognition studies are briefly discussed.