Color singleton pop-out does not always poop out: An alternative to visual search

Folk psychology suggests that when an observer views a scene, a unique item will stand out and draw attention to itself. This belief stands in contrast to numerous studies in visual search that have found that a unique target item (e.g., a unique color) is not identified more quickly than a nonunique target. We hypothesized that this finding is the result of task demands of visual search, and that when the task does not involve visual search, uniqueness will pop out. We tested this hypothesis in a task in which observers were presented an array of letters and asked to respond aloud, as quickly as possible, with the identity of any one of the letters. The observers were significantly more likely to respond with a uniquely colored letter than would be expected by chance. In a task in which observers blurt out the first thing that they see, unique pop-out does not poop out.     

Age differences in target identification as a function of retinal location and noise level: examination of the useful field of view

Foveal and peripheral target detection were compared in young adults (M age = 22 years) and older adults (M age = 66 years) who were optically corrected for the viewing distance. In a two-alternative, forced-choice task, target letters were presented at 0 degree to 10.5 degrees from fixation. Targets were presented alone, flanked on each side by one noise element (i.e., nontarget letter), or embedded in a horizontal row of 19 noise elements. An Age X Noise Level X Location interaction was obtained, wherein age differences were largest for peripheral targets presented in noise. Slope analyses of latency data showed that the performance of young adults in the high-noise condition was most similar to that of older adults in the low-noise condition. At the functional level, results indicated that aging is associated with a restricted useful field of view. In addition, the data suggest that age differences in search can be described by a model in which older adults take smaller perceptual samples from the visual scene and scan these samples more slowly than do the young adults.     

Letter search through words and nonwords: The effect of fixed,absent, or mutilated targets

The present study attempted to eliminate the word superiority effect found in letter search by holding the target letter fixed across trials. The expectation was that the target would thereby become so familiar and salient that the subject would "see" only that letter during search. Even with the target-letter held fixed (Experiment I), however, search was still faster through words than through nonwords, indicating that nontarget letters had been "seen" as well. Search also remained faster through words than through nonwords when the number of exposures to the target was further increased by having the subject search for the absence rather than the presence of the target letter (Experiment III). In line with the notion of "proofreader's errors," however, search became relatively more accurate on nonwords than on words when it required detection of the "mutilation" produced by substituting an F for an E, e.g., BASKFT, BAKFRY (Experiment IV).     

The effects of the binocular disparity differences between targets and maskers on visual search

A visual search for targets is facilitated when the target objects are on a different depth plane than other masking objects cluttering the scene. The ability of observers to determine whether one of four letters presented stereoscopically at four symmetrically located positions on the fixation plane differed from the other three was assessed when the target letters were masked by other randomly positioned and oriented letters appearing on the same depth plane as the target letters, or in front, or behind it. Three additional control maskers, derived from the letter maskers, were also presented on the same three depth planes: (1) random-phase maskers (same spectral amplitude composition as the letter masker but with the phase spectrum randomized); (2) random-pixel maskers (the locations of the letter maskers’ pixel amplitudes were randomized); (3) letter-fragment maskers (the same letters as in the letter masker but broken up into fragments). Performance improved with target duration when the target-letter plane was in front of the letter-masker plane, but not when the target letters were on the same plane as the masker, or behind it. A comparison of the results for the four different kinds of maskers indicated that maskers consisting of recognizable objects (letters or letter fragments) interfere more with search and comparison judgments than do visual noise maskers having the same spatial frequency profile and contrast. In addition, performance was poorer for letter maskers than for letter-masker fragments, suggesting that the letter maskers interfered more with performance than the letter-fragment maskers because of the lexical activity they elicit.     

Reaction time in reading a tachistoscopic display for a memory set item

Reaction times were measured in a task which requires the subject to search a brief visual array for a critical letter embedded in a row of background letters. In Experiment 1, the position of a critical letter in an instructed reading order and the size of a set of memorized letters were varied. Mean reaction time increased monotonically with distance of the critical letter from the beginning of the instructed reading path in the display. The variables reading position and memory set size were additive in their effect on mean reaction time. Data from a second experiment in which the retinal location of the critical letter and its reading position were varied showed that both reading position and retinal location influenced mean reaction time, but the effect of reading position on reaction time was greater. These variables interacted.     

Evidence for an addition to the reading scan hypothesis

Letters were tachistoscopically presented in pairs to the left or right of fixation for 40 msec. The pair consisted of a target letter (B, D, P, or T) and a noise letter (all other letters of the alphabet except I), with the noise letter appearing either to the inside or the outside of the stimulus letter. S’s task was to report verbally the target letter as fast as possible. Reaction times and number of errors indicated that there was more interference when the noise letter occurred further from the fixation point than the target letter for both the left and right visual field. Since a reading scan cannot account for the results in the right visual field, an outside-toward-fixation scan is proposed. An analysis of the different kinds of errors indicated that the outside to fixation scan is more primitive than the reading scan in that it produces less detailed information about the letters than does the reading scan.     

Flank to the left,flank to the right: Testing the modified receptive field hypothesis of letter-specific crowding

The present study tested for effects of number of flankers positioned to the left and to the right of target characters as a function of visual field and stimulus type (letters or shapes). On the basis of the modified receptive field hypothesis (Chanceaux & Grainger, 2012), we predicted that the greatest effects of flanker interference would occur for leftward flankers with letter targets in the left visual field. Target letters and simple shape stimuli were briefly presented and accompanied by either 1, 2, or 3 flankers of the same category either to the left or to the right of the target, and in all conditions with a single flanker on the opposite side. Targets were presented in the left or right visual field at a fixed eccentricity, such that targets and flankers always fell into the same visual field. Results showed greatest interference for leftward flankers associated with letter targets in the left visual field, as predicted by the modified receptive field hypothesis.     

Letter and word code interactions elicited by normally displayed words

The dependence of visual word recognition on letter processing was investigated by measuring the effect of a cue word on subsequent target word processing for various degrees of cue/ target similarity. Using a simultaneous matching task (Experiments 1 and 2), modest facilitation was found for identical cue/target items only, whereas items that differed by a single letter led to substantial interference. Targets that shared internal or external letters with cues yielded latencies comparable to those for neutral or different cue conditions. The identical facilitation and high-similarity interference was also found in a lexical decision task under normal display conditions (Experiment 3). However, when direct letter processing was measured using spatially transformed targets (Experiment 4), large facilitatory effects were found for similar as well as for identical cue/target conditions. Although both letter and word codes appear to be activated by normally displayed words, such word code activity may not routinely depend upon letter code outputs.     

Whole-word units are used before orthographic knowledge in perceptual development

A visual search task for target letters in multiletter displays was used to investigate information-processing differences between college students and presecond-grade children (mean age = 7 years, 4 months). The stimulus displays consisted of single words, pronounceable pseudowords, and unpronounceable nonwords varying in length from three to five letters. The mean response times for indicating whether or not a target letter occurred in the display increased with the number of display letters for both groups, although there were apparent differences between groups in the rate of search and type of search strategy used. Pre-second-grade children responded faster to word displays than to pseudoword and nonword displays, indicating that familiar letter strings could be processed faster than unfamiliar strings regardless of whether or not the latter were consistent with rules of English orthography. In contrast, college students processed words and pseudowords about equally well, and both resulted in faster responses than nonwords. As reading skills develop, children apparently come to process familiar words differently from other letter strings. Only after a significant sightword vocabulary is established do children seem to recognize the regularities of standard English orthography and make use of this knowledge to facilitate perceptual processes.     

Category-level contributions to the alphanumeric category effect in visual search

Do letter and digit recognition depend on the same or different cognitive mechanisms? Letters are detected more quickly among digits than among letters; likewise, digit search is facilitated when distractors are letters, as opposed to digits. This effect suggests that different mechanisms underlie recognition of these two categories. There are, however, systematic physical differences between letters and digits that might account for the effect. We used target and distractor stimuli that facilitated within-category search when inverted, and category identity was, thereby, attenuated. However, in conditions of upright search, in which category identity was more salient, between-category search was more efficient for the same stimuli. These findings suggest that letter and digit recognition are, at least to a degree, functionally independent.     

Detection of intraword and interword letter repetition: A test of the word unitization hypothesis

Do words, as familiar units or gestalts, tend to swallow up and conceal their letter components (Pillsbury, 1897)? Letters typically are detected faster and more accurately in words than in nonwords (i.e., scrambled collections of letters), and in more frequent words than in less frequent words. However, a word advantage at encoding, where the representation of the string is formed, might compensate for, and thus mask, a word disadvantage at decoding and comparison, where the component letters of the representation are accessed and compared with the target letter. To better reveal any such word disadvantage, a task was used in this study that increased the amount of letter processing. Subjects judged whether a letter was repeated within a six-letter word or a nonword (Experiment 1; intraword letter repetition) or was repeated between two adjacent unrelated six-letter words or nonwords (Experiment 2; interword letter repetition). Contrary to Pillsbury's word unitization hypothesis, both types of letter repetition (intraword and interword) were detected faster and just as accurately with words as with nonwords. In Experiment 2, however, interword letter repetition was detected less accurately on common words (but not on rare words or third-order pseudowords) than on the corresponding nonwords. Thus, although the familiar word does not deny access to its own component letters, it does make their comparison with letters from other words more difficult.     

Vibrotactile letter recognition: The effects of a ma king stimulus

A series of experiments examined the effect of masking stimuli on the ability of observers to recognize letters of the alphabet through their fingertips. The letters were generated on the 6 × 24 vibrotactile array of the Optacon, a reading aid for the blind. Letter recognition was interfered with by the presence of masking stimuli occurring at the same site on the skin either before (forward masking) or after (backward masking) the target letter had been presented. In general, backward masking interfered with letter recognition more than did forward masking. Backward masking was particularly effective for letters in which the information critical for identification is located on the right side of the letter. Presenting the letters reversed resulted in more forward masking for those letters with critical information now located on the left side. Increasing the time between the target letter and the masking stimuli resulted in improved letter recognition. The implications of the results for tactile reading are discussed.     

Response latency in visual search with redundancy in the visual display

Two experiments were run to investigate the effects of redundant display items upon response latency in a visual search task. In the first study, Ss searched five-letter displays for a predesignated critical letter. Both critical and noncritical letters could be repeated in the displays. Mean response latency decreased markedly with increasing redundancy in the critical letter and was affected to a lesser extent by redundancy in the noncritical letters. In the second study, Ss were required to detect the presence of redundant letters in displays of from two to five letters, first with no information as to what letter might be repeated, then with knowledge of which letter would be repeated if the display contained a redundant letter. Response latencies in the former case were much slower than in the latter. The implications of these findings for current views of visual information processing were discussed.     

The category effect in visual search depends on physical rather than conceptual differences

Is a target letter (digit) more readily detected in a digit (letter) background because of conceptual-level differences between letters and digits or because of physical-level differences? When letters and digits were matched on physical features, both for the target set and the background set, no letter vs. digit category effect was found. With physical differences eliminated, search was faster and more accurate for letter than for digit targets and distractors, presumably because of the greater familiarity of letters. Presenting the same characters in normal and mirrorreversed orientation, which also minimized featural differences between categories, produced only a small normal vs. reversed category effect. In a normal background, a reversed target lost much more from its unfamiliarity than it gained from mismatching the background. The present results indicate that the category effect vanishes when only conceptual level differences are present.     

Global-local orientation congruency effects in visual search

In a visual search task, subjects had to decide which of 2 possible target letters was presented among 12 distractor letters. The 13 characters were arranged to form a global Navon-type letter. The global letter and the local letters (target and distractors) were independently presented in four different viewer-related orientations. When the global letter and the target were frequently congruently oriented, the response times increased with growing orientation disparity between them. This global-target congruency effect was independent from target identity (Experiment 1), and it diminished when global and target orientations were not correlated (Experiment 2). The results indicate that the orientation of the global letter can be deliberately used in order to facilitate the processing of congruently oriented local targets. The alignment of a spatial frame of reference is discussed as the most probable process underlying this facilitation.     

The effect of a visual indicator on rate of visual search: Evidence for processing control

Search rates were estirnated from response latencies in a visual search task of the type used by Atkinson, Holmgren, and Juola (1969), in which a S searches a small set of letters to determine the presence or absence of a predesignated target. Half of the visual displays contained a marker above one of the letters. The marked letter was the only one that had to be checked to determine whether or not the display contained the target. The presence of a marker in a display significantly increased the estimated rate of search, but the data clearly indicated that Ss did not restrict processing to the marked item. Letters in the vicinity of the marker were also processed. These results were interpreted as showing that Ss are able to exercise some degree of control over the search process in this type of task.     

掩蔽刺激对目标识别加工的作用：来自fNIRS的证据

信息掩蔽刺激(如随机字母群)对字母视觉搜索的干扰大于能量掩蔽刺激(如将字母群像素随机化后的散点), 但相应的中枢机理还不清楚。本研究采用记录脑代谢激活模式的功能性近红外光学脑成像技术(fNIRS), 考察年轻成年被试分别在字母掩蔽、字母碎片掩蔽、像素掩蔽条件下判断上、下、左、右四个目标字母是否相同时的大脑皮层氧合血红蛋白浓度的变化。结果显示, 依字母、字母碎片、随机散点掩蔽条件顺序, 被试的搜索任务成绩显著递增, 而顶-枕皮层的激活范围与程度显著递减, 表明信息掩蔽较匹配的能量掩蔽对视觉搜索有更大的干扰作用, 并在初级和联合视觉皮层引发更大的激活。在字母碎片掩蔽条件下, 视觉初级皮层部分区域的激活水平与搜索行为绩效的相关显著, 而在字母掩蔽条件下, 视觉联合皮层部分区域的激活水平与搜索行为绩效的相关显著。这进一步说明信息掩蔽中的字母掩蔽和字母碎片掩蔽的掩蔽作用在大脑皮层上所造成的加工负载存在差异。     

Direct assessments of the processing time hypothesis for the missing-letter effect

When participants search for a target letter while reading, they make more omissions if the target letter is embedded in frequently used words or in the most frequent meaning of a polysemic word. According to the processing time hypothesis, this occurs because familiar words and meanings are identified faster, leaving less time for letter identification. Contrary to the predictions of the processing time hypothesis, with a rapid serial visual presentation procedure, participants were slower at detecting target letters for more frequent words or the most frequent meaning of a word (Experiments 1 and 2) or at detecting the word itself instead of a target letter (Experiment 3). In Experiments 4 and 5, participants self-initiated the presentation of each word, and the same pattern of results was observed as in Experiments 1 and 3. Positive correlations were also found between omission rate and response latencies.     

Color segregation and selective attention in a nonsearch task

Relations between selective attention and perceptual segregation by color were investigated in binary-choice reaction time experiments based on the non search paradigm of Eriksen and Eriksen (1974). In focused attention conditions (Experiment 1), noise letters flanking a central target letter caused less interference when they differed from the target in color, although color carried no information as to whether or not a letter was the target. When blocking of trials favored a strategy of dividing attention between target and noise letters (Experiment 2), no benefit accrued from difference between target color and noise color. The results supported an attentional interpretation of the effect of color demonstrated in Experiment 1, implying that perceptual segregation by color improved the efficiency of focusing attention on the target.     

Levels of processing in disruptive effects of prior information

Under certain conditions, advance information about possible letter alternatives may depress recognition of single tachistoscopically presented letters followed by a pattern mask. Neill and Walling (1981) found that this “before-disruption effect” occurred specifically when alternatives were featurally similar. In contrast, Experiment 1 of the present study found that precuing facilitated identification of unfamiliar stimuli composed of letterlike features, particularly when alternatives differed in only one critical feature. Contrary to Smith, Haviland, Reder, Brownell, and Adams (1976), composition of letterlike features is therefore not sufficient to produce the before-disruption effect. The before-disruption effect appears to occur when there is opportunity to represent the stimulus at a deeper (i.e., name) level, but foreknowledge of a critical distinguishing feature biases processing instead toward the level of physical features. Congruent with this analysis, Experiment 2 found the before-disruption effect for letters to be attenuated when targets were unpredictably upper- and lowercase, necessitating name-level matching to the alternatives. Experiment 3 found the superior identification of unprecued letters to be paradoxically associated with inferior target detection, as indicated by concurrent presence/absence judgments. In addition, identification of unprecued letters, but not precued letters, was significantly above chance on trials in which overt target detection failed to occur. The results are consistent with recent suggestions that pattern masking does not terminate perceptual processing, but rather interferes with conscious awareness of completed visual analysis.