An important component of routine visual behavior is the ability to find one item in a visual world filled with other, distracting items. This ability to performvisual search has been the subject of a large body of research in the past 15 years. This paper reviews the visual search literature and presents a model of human search behavior. Built upon the work of Neisser, Treisman, Julesz, and others, the model distinguishes between a preattentive, massively parallel stage that processes information about basic visual features (color, motion, various depth cues, etc.) across large portions of the visual field and a subsequent limited-capacity stage that performs other, more complex operations (e.g., face recognition, reading, object identification) over a limited portion of the visual field. The spatial deployment of the limited-capacity process is under attentional control. The heart of the guided search model is the idea that attentional deployment of limited resources isguided by the output of the earlier parallel processes. Guided Search 2.0 (GS2) is a revision of the model in which virtually all aspects of the model have been made more explicit and/or revised in light of new data. The paper is organized into four parts: Part 1 presents the model and the details of its computer simulation. Part 2 reviews the visual search literature on preattentive processing of basic features and shows how the GS2 simulation reproduces those results. Part 3 reviews the literature on the attentional deployment of limited-capacity processes in conjunction and serial searches and shows how the simulation handles those conditions. Finally, Part 4 deals with shortcomings of the model and unresolved issues.

/pdf/guided-search-2-0-a-revised-model-of-visual-search-1qi4v6qhev.pdf

Guided Search 2.0 A revised model of visual search

1. The activity of single neurons was recorded in Macaca mulatta monkeys while they performed tasks requiring them to select a cued stimulus from an array of three to eight stimuli and report the orientation of that stimulus. Stimuli were presented in a circular array centered on the fixation target and scaled to place a single stimulus element within the receptive field of the neuron under study. The timing of the cuing event permitted the directing of visual attention to the spatial location of the correct stimulus before its presentation. 2. The effects of focal attention were examined in cortical visual areas V1, V2, and V4, where a total of 672 neurons were isolated with complete studies obtained for 94 V1, 74 V2, and 74 V4 neurons with receptive-field center eccentricities in the range 1.8-8 degrees. Under certain conditions, directed focal attention results in changes in the response of V1, V2, and V4 neurons to otherwise identical stimuli at spatially specific locations. 3. More than one-third of the neurons in each area displayed differential sensitivity when attention was directed toward versus away from the spatial location of the receptive field just before and during stimulus presentation. Both relative increases and decreases in neural activity were observed in association with attention directed at receptive-field stimuli. 4. The presence of multiple competing stimuli in the visual field was a major factor determining the presence or absence of differential sensitivity. About two-thirds of the neurons that were differentially sensitive to the attending condition in the presence of competing stimuli were not differentially sensitive when single stimuli were presented in control studies. For V1 and V2 neurons the presence of only a few (3-4) competing stimuli was sufficient for a majority of the neurons studied; a majority of the V4 neurons required six to eight stimuli in the array before significant differences between attending conditions occurred. 5. For V1 and V2 neurons the neuronal sensitivity differences between attending conditions were observed primarily at or near the peak of the orientation tuning sensitivity for each neuron; the differences were evident over a broader range of orientations in V4 neurons. 6. In conclusion, neural correlates of focal attentive processes can be observed in visual cortical processing in areas V1 and V2 as well as area V4 under conditions that require stimulus feature analysis and selective spatial processing within a field of competing stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Focal attention produces spatially selective processing in visual cortical areas V1, V2, and V4 in the presence of competing stimuli.

Perception and discrimination as a function of stimulus orientation: The "oblique effect" in man and animals.

Crowding—An essential bottleneck for object recognition: A mini-review

A shape can be more difficult to identify when other shapes are near it. For example, when several grating patches are viewed parafoveally, observers are unable to report the orientation of the central patch. This phenomenon, known as 'crowding,' has historically been confused with lateral masking, in which one stimulus attenuates signals generated by another stimulus. Here we show that despite their inability to report the orientation of an individual patch, observers can reliably estimate the average orientation, demonstrating that the local orientation signals are combined rather than lost. Our results imply that crowding is distinct from ordinary masking, and is perhaps related to texture perception. Under crowded conditions, the orientation signals in primary visual cortex are pooled before they reach consciousness.

/pdf/compulsory-averaging-of-crowded-orientation-signals-in-human-2y0lx65wyu.pdf

Compulsory averaging of crowded orientation signals in human vision

https://pure.tue.nl/ws/files/4267560/734493.pdf

Eccentric vision: adverse interactions between line segments.

Perceived orientation of isolated line segments

Induced changes in the perceived orientation of line segments

Perceived orientation ? of a line stimulus presented in a frontal plane deviates systematically from the geometrical slant a of the line stimulus. In fact, ? is biassed a few degrees towards the horizontal H or vertical V, whichever is nearest (Bouma and Andriessen, 1968a). If a second line stimulus is present, an extra bias occurs, usually towards the perpendicular of the second line (Bouma and Andriessen, 1970). In the measurements referred to above, the subjects adjusted a dot in line with the test line. The accuracy of observation is reflected in the standard deviation of the settings (of the order of 10 ). It is relatively low for H and V and high for obliques (Bouma and Andriessen, 1968a). In working towards a theory of slant perception (Bouma and Andriessen, 1968b), we aimed at including systematic bias effects as well as accuracies of observation. Since in the method of adjustment each setting might have been based on more than one stimulus presentation, we switched for measuring accuracies to a method in which each response can be attributed to a single presentation. We chose a sequential up-and-down method (Cardozo, 1966) in which the subject had to report on the slant difference of two successive test line presentations. Roughly, we found results similar to those of the method of adjustment. In the meantime we got interested in eccentric vision, where a starting point has been found for processes of visual search (Engel, 1969) and of form interaction (Bouma, 1970; Beerens and Bouma, 1970). This made us wonder how much the accuracy of slant observation decreases with increasing eccentricity of the line stimulus. We report here on some exploratory measurements on the latter question.

JJ Andriessen

Papers

Eccentric vision: adverse interactions between line segments.

Perceived orientation of isolated line segments

Induced changes in the perceived orientation of line segments

Just noticeable differences in slant of test lines as a function of retinal eccentricity

Induced changes in perceived orientation