Probability matching in visual selective attention

Jonides (1980, p. 111) suggested a model to account for shifts of spatial attention in visual search tasks with less than 100% cue validity. This two-stage probability matching model was subsequently tested by Jonides (1983). Reaction time distribution characteristics indeed provided some support for the model. In the present paper the relevant data presented in Jonides (1980, 1981, 1983) are further analysed. The results of this analysis strongly support the probability matching hypothesis. Probability matching is apparently a very important strategic characteristic of visual spatial attention that deserves much more study.     

Perceptual grouping and visual selective attention

The present study demonstrates that incongruent distractor letters at a constant distance from a target letter produce more response competition and negative priming when they share a target’s color than when they have a different color. Moreover, perceptual grouping by means of color, attenuated the effects of spatial proximity. For example, when all items were presented in the same color, near distractors produced more response competition and negative priming than far distractors (Experiment 3A). However, when near distractors were presented in a different color and far distractors were presented in the same color as the target, the response competition × distractor proximity interaction was eliminated and the proximity × negative priming interaction was reversed (Experiment 3B). A final experiment demonstrated that distractors appearing on the same object as a selected target produced comparable amounts of response competition and negative priming whether they were near or far from the target. This suggests that the inhibitory mechanisms of visual attention can be directed to perceptual groups/objects in the environment and not only to unsegmented regions of visual space.     

Food pleasantness affects visual selective attention

Fundamental to adaptive behaviour is the ability to select environmental objects that best satisfy current needs and preferences. Here we investigated whether temporary changes in food preference influence visual selective attention. To this end, we exploited the fact that when a food is eaten to satiety its motivational value and perceived pleasantness decrease relative to other foods not eaten in the meal, an effect termed sensory-specific satiety. A total of 26 hungry participants were fed until sated with one of two palatable foods. Before and after selective satiation, participants rated the pleasantness of the two foods and then viewed the same as stimuli on a computer screen while attention was assessed by a visual probe task. Results showed that the attentional bias for the food eaten decreased markedly from pre- to postsatiety, along with the subjective pleasantness for that food. By contrast, subjective pleasantness and attentional bias for the food not eaten did not show any such decrease. These findings suggest that the allocation of visual selective attention is flexibly and rapidly adjusted to reflect temporary shift in relative preference for different foods.     

Evoked potential correlates of visual selective attention

Two experiments are reported in which the relationship is explored between the N1 and P2 components of the visual evoked potential and visual selective attention. In both experiments, channels were defined in terms of stimulus attributes (experiment 1 — intensity; experiment 2 — shape) with all stimuli being presented at a common spatial locus in order to preclude fixation shifts. Under these circumstances, P2 was found in both experiments to correlate with visual selective attention whereas N1 did not. It is concluded from the null result for N1 that a precortical gating mechanism for visual inputs within a single spatial channel is not a component of the visual system. The P2 correlate of visual selective attention, because of its long latency, is attributed to the differential post-perceptual processing inevitably received by task-relevant and task-irrelevant inputs.     

Object-based visual selective attention and perceptual organization

We report the results of four experiments that were conducted to examine both the representations that provide candidate entities available for object-based attentional selection and the influence of bottom-up factors (i.e., geometric and surface characteristics of objects) and top-down factors (i.e., context and expectancies) on the selection process. Subjects performed the same task in each of the experiments. They were asked to determine whether two target properties, a bent end and an open end of a wrench, appeared in a brief display of two wrenches. In each experiment, the target properties could occur on a single wrench or one property could occur on each of two wrenches. The question of central interest was whether a same-object effect (faster and/or more accurate performance when the target properties appeared on one vs. two wrenches) would be observed in different experimental conditions. Several interesting results were obtained. First, depending on the geometric (i.e., concave discontinuities on object contours) and surface characteristics (i.e., homogeneous regions of color and texture) of the stimuli, attention was preferentially directed to one of three representational levels, as indicated by the presence or absence of the same-object effect. Second, although geometric and surface characteristics defined the candidate objects available for attentional selection, top-down factors were quite influential in determining which representational level would be selected. Third, the results suggest that uniform connectedness plays an important role in defining the entities available for attention selection. These results are discussed in terms of the manner in which attention selects objects in the visual environment.     

Gamma activity in human EEG is related to highspeed memory comparisons during object selective attention

Among the most important processes of the brain in order to correctly perceive the outside world and act within it are binding, attention, and memory. All three functional mechanisms have been associated with brain activity in the gamma frequency range. It needs to be clarified, however, which subprocesses within the gamma frequency range relate to which perceptual or cognitive functions. In a visual discrimination task, we used Kanizsa figures whose constituent inducer disks need to be bound together to perceive the illusory contours. By a variation of the task requirements we manipulated the allocation of object selective attention as compared to a previous study. One out of four objects had to be detected. This detection process requires the comparison of two object dimensions (form and collinearity) with a working memory template. In order to get behavioural and electrophysiological measures, EEG and reaction times were recorded from 16 and 10 subjects, respectively. We demonstrated that the early evoked gamma activity reflects the process of allocating attention to a selected object as early as 50-150 ms after stimulus onset. We propose that the underlying mechanism is a high-speed memory comparison. In addition, we show that this early gamma activity also determines the reaction times needed to respond to the different stimuli.     

Acquisition of habitual visual attention and transfer to related tasks

Extensive research has shown that statistical learning affects perception, attention, and action control; however, few studies have directly linked statistical learning with the formation of habits. Evidence that learning can induce a search habit has come from location probability learning, in which people prioritize locations frequently attended to in the past. Here, using an alternating training–testing procedure, we demonstrated that the initial attentional bias arises from short-term intertrial priming, whereas probability learning takes longer to emerge, first reaching significance in covert orienting (measured by reaction times) after about 48 training trials, and in overt orienting (measured by eye movements) after about 96 training trials. We further showed that location probability learning is persistent after training is discontinued, by transferring from a letter search task to a scene search task—emulating another characteristic feature of habits. By identifying the onset of probability learning and investigating its task specificity, this study provides evidence that probability cuing can induce habitual spatial attention.     

Effect of target separation on selective attention.

A visual search task, in which subjects searched circular stimulus displays for two instances of a prespecified target, was used to investigate the effects of target-separation on accuracy. When a comparison was made of the total number of targets correctly located at each separation, no significant differences were found, and this suggested that, within the range of separations (maximum of 2.53 degrees) examined, the selective processing of the relevant items was not influenced by the distance separating them. Also, assuming that the redundancy of target items increased the probability of a target being perceived, the differences between the number of first targets correctly located and the number correct in a single target condition, were in the predicted direction. However, they failed to reach significance.     

Developmental changes in selective and integrative visual attention

School-aged children and adults performed two speeded classification tasks designed to examine the relation between selective and integrative aspects of visual attention. Stimuli consisted of two parentheses (Experiment 1) or two arrows (Experiment 2) separated by 0.5 to 16 degrees visual angle. In a selective attention task, observers classified stimuli on the basis of one of the two elements. Younger children experienced more interference when the elements were closely spaced than older children and adults. In an integrative attention task, stimuli were classified on the basis of both of the elements. Here age differences were most pronounced when elements were separated by large visual angles. These findings suggest that the ability to contract and expand the size of the attentional "spotlight" improves with age in the school years.     

Interactions between visual working memory and selective attention

The relationship between working memory and selective attention has traditionally been discussed as operating in one direction: Attention filters incoming information, allowing only relevant information into short-term processing stores. This study tested the prediction that the contents of visual working memory also influence the guidance of selective attention. Participants held a sample object in working memory on each trial. Two objects, one matching the sample and the other novel, were then presented simultaneously. As measured by a probe task, attention shifted to the object matching the sample. This effect generalized across object type, attentional-probe task, and working memory task. In contrast, a matched task with no memory requirement showed the opposite pattern, demonstrating that this effect is not simply due to exposure to the sample. These results confirm a specific prediction about the influence of working memory contents on the guidance of attention.     

Top-down selective visual attention: A neurodynamical approach

We propose a system of interconnected modules consisting of populations of neurons for modelling the underlying mechanisms involved in selective visual attention. We demonstrate that it is plausible to build a neural system for visual search, which works across the visual field in parallel, but, due to the intrinsic dynamics of the system, resembles apparent modes of visual attention, namely the serial focal and the parallel spread over the space mode. Thus, neither explicit serial focal search nor saliency maps need to be assumed. A focal attentional spotlight is not included in the system but rather focal attention emerges due to the convergence of the dynamic behaviour of the neural networks. The dynamics of the system can be interpreted as a mechanism for routing information from the sensory input.     

Distinguishing blocking from attenuation in visual selective attention

Sensory information must be processed selectively in order to represent the world and guide behavior. How does such selection occur? Here we consider two alternative classes of selection mechanisms: In blocking, unattended stimuli are blocked entirely from access to downstream processes, and in attenuation, unattended stimuli are reduced in strength but if strong enough can still access downstream processes. Existing evidence as to whether blocking or attenuation is a more accurate model of human performance is mixed. Capitalizing on a general distinction between blocking and attenuation-blocking cannot be overcome by strong stimuli, whereas attenuation can-we measured how attention interacted with the strength of stimuli in two spatial selection paradigms, spatial filtering and spatial monitoring. The evidence was consistent with blocking for the filtering paradigm and with attenuation for the monitoring paradigm. This approach provides a general measure of the fate of unattended stimuli.     

Abrupt visual onsets and selective attention: evidence from visual search

The effect of temporal discontinuity on visual search was assessed by presenting a display in which one item had an abrupt onset, while other items were introduced by gradually removing line segments that camouflaged them. We hypothesized that an abrupt onset in a visual display would capture visual attention, giving this item a processing advantage over items lacking an abrupt leading edge. This prediction was confirmed in Experiment 1. We designed a second experiment to ensure that this finding was due to attentional factors rather than to sensory or perceptual ones. Experiment 3 replicated Experiment 1 and demonstrated that the procedure used to avoid abrupt onset--camouflage removal--did not require a gradual waveform. Implications of these findings for theories of attention are discussed.     

The control of visual attention using multiple target features

An experiment was conducted to determine how visual attention is allocated in response to pairwise combinations of location, color, and size cues. Subjects viewed displays of eight letters arranged into an 'X' pattern emanating from a central fixation point. The letters varied on the dimensions of location (foveal or parafoveal positions), size (large or small), and color (red or blue). Seven of the letters were 'X's and the remaining, critical letter was either an 'R' or an 'L'. Subjects were given advance cues about characteristics of the critical letter on two of the three dimensions (location size, and color). The cues varied in their validity such that on any trial either both dimensions were validly cued, one dimension was validly cued while the other was invalidly cued, or both cues were invalid. Subjects were instructed to try to use the cues to find the critical letter, and response times to identify it as an 'R' or an 'L' served as the main dependent measure. Two models were evaluated against the data; in one, location cues are viewed as having distinct effects on an early stage of attention whereas color and size cues operate only in a later, selection stage. In the other model, all cues are used in a similar way to select display items for serial, focal attention. In general, the serial processing model provides a more complete account of the data.     

Cross-modal selective attention: on the difficulty of ignoring sounds at the locus of visual attention

In three experiments, we investigated whether the ease with which distracting sounds can be ignored depends on their distance from fixation and from attended visual events. In the first experiment, participants shadowed an auditory stream of words presented behind their heads, while simultaneously fixating visual lip-read information consistent with the relevant auditory stream, or meaningless "chewing" lip movements. An irrelevant auditory stream of words, which participants had to ignore, was presented either from the same side as the fixated visual stream or from the opposite side. Selective shadowing was less accurate in the former condition, implying that distracting sounds are harder to ignore when fixated. Furthermore, the impairment when fixating toward distractor sounds was greater when speaking lips were fixated than when chewing lips were fixated, suggesting that people find it particularly difficult to ignore sounds at locations that are actively attended for visual lipreading rather than merely passively fixated. Experiments 2 and 3 tested whether these results are specific to cross-modal links in speech perception by replacing the visual lip movements with a rapidly changing stream of meaningless visual shapes. The auditory task was again shadowing, but the active visual task was now monitoring for a specific visual shape at one location. A decrement in shadowing was again observed when participants passively fixated toward the irrelevant auditory stream. This decrement was larger when participants performed a difficult active visual task there versus fixating, but not for a less demanding visual task versus fixation. The implications for cross-modal links in spatial attention are discussed.