Visual attention and stimulus identification

Previous research has provided evidence for parallel stimulus processing in visual search tasks; however, it has frequently been noted that detecting prespecified targets might be accomplished without actually identifying targets and/or distractors. A novel task was employed to require exhaustive identification: Subjects named the highest digit in an array. Reaction times and display size effects in this task were strikingly similar to the conventional search tasks reported here. Manipulation of display size and visual quality was used to test predictions of serial versus parallel encoding models. Display size was additive with two different visual quality factors in the highest digit task, a finding that argues against serial execution of the corresponding stages. Interactions with decision-related factors suggest that visual quality may have affected the rate of character recognition, not just feature extraction. Thus, various aspects of the results seem to strengthen the case for parallel (though perhaps capacity-limited) identification of multiple familiar stimuli. In the General Discussion, it is pointed out that parallel identification need not entail late selection, and some alternative possibilities are suggested.     

Hemispheric differences in stimulus identification

Subjects were presented with either verbal (letters) or nonverbal (outline forms) stimuli to their left or right cerebral hemispheres. Verbal items presented with a lateral masking stimulus were identified more quickly and accurately when presented to the right hemisphere rather than to the left. When the letters were presented without a masking stimulus, weak hemispheric effects were obtained. Nonverbal forms demonstrated faster reaction time and fewer errors for right-hemisphere presentations under both masked and unmasked conditions. Retinal locus of the display item was also varied and produced faster responding with fewer errors when the stimulus was presented foveally rather than peripherally under all display conditions. These effects were attributed to the use of a manual response procedure that effectively reduced the ability of subjects to employ names for the stimulus objects.     

Regulatory fit effects on stimulus identification

This article examines the effects of a fit between a person's global regulatory focus and the local task reward structure on perceptual processing and judgment. On each trial, participants were presented with one of two briefly presented stimuli and were asked to identify it. Participants were placed in a promotion focus (a situationally induced sensitivity to gains) or a prevention focus (a situationally induced sensitivity to losses) and were asked to maximize gains or minimize losses. An asymmetric payoff ratio biased the overall reward toward one identification response over the other. Two experiments tested the role of regulatory fit when internal familiarity and perceptual sensitivity were low or high. When familiarity and sensitivity were low, participants in a regulatory fit (promotion focus with gains or a prevention focus with losses) showed greater perceptual sensitivity but no response bias differences, relative to participants in a regulatory mismatch. When familiarity and sensitivity were high, participants in a regulatory fit showed a response bias toward the high-payoff stimulus but no differences in perceptual sensitivity. Speculations are offered on the neurobiological basis of this effect, as well as implications of this work for clinical disorders such as depression.     

Priming outside of awareness and subsequent stimulus identification.

The influence of priming outside of awareness on performance of a color-recognition task was investigated. Using a tachistoscope, a color word that matched ("congruent prime") or did not match ("incongruent prime") the target color or a blank prime was followed by a pattern mask and the target color. Identification performance was superior on the blank prime trials to the congruent prime trials, with performance on the incongruent prime trials being the lowest. A subsequent study included a meaningless (XXX) prime condition, and it was found that meaningless primes interfered with target-color identification more than the congruent and blank prime conditions, but less than the incongruent prime condition, suggesting that primes, in addition to producing semantic activation, impose demands on information-processing capacity of the perceptual system.     

Visual identification rate in search of a missing stimulus

Subjects searched for a digit which was not presented in an array of nine different digits. The identification rate was estimated from the percent correct. Well-trained subjects identified 6.5 digits with a 50-msec. exposure. This fast identification rate was expected from our procedure using a single answer, an inconsistent target, and equal probability that every digit would be a target. Naive subjects markedly improved their performance in the first two weeks of the trials which were given for a total of 24 days.     

Independent dimension-weighting mechanisms for visual selection and stimulus identification

Observers respond faster when the task-relevant perceptual dimension (e.g., color) repeats across consecutive trials relative to when it changes. Such dimension repetition benefits (DRBs) occur in different tasks, from singleton feature search to feature discrimination of a stimulus presented on its own. Here, we argue that the DRBs observed in different tasks originate from distinct mechanisms: preselective weighting of dimension-specific feature contrast signals and, respectively, postselective stimulus processing. The multiple-weighting-systems hypothesis predicts significant DRBs across trials of different tasks that share the same weighting mechanism, but not across tasks involving different mechanisms. Experiments 1, 2, and 3 examined DRBs across localization and detection tasks (both involving feature contrast computations); across detection and identification tasks (which presumably involved different weighting systems); and across identification and discrimination tasks (both involving stimulus identification). As expected, significant DRBs were observed across different tasks in Experiments 1 and 3, but not in Experiment 2. These findings support the multiple-weighting-systems hypothesis.     

Attribute identification in children as a function of stimulus dimensionality

Thirty-two four-year-old and 32 six-year-old children were presented a conjunctive concept that involved either two values from within a single dimension (unidimensional condition) or two values from different dimensions (bidimensional condition). As predicted, the results showed that the uni- vs bidimensional factor had no effect upon the performance of the younger children, while the older children solved more rapidly in the unidimensional than in the bidimensional condition. The results were interpreted to suggest that the younger children's responding is not under dimensional control and that a major source of difficulty for older children solving the conjunctive concept is the necessity of responding to two dimensions, not to two values.     

Effects of stimulus duration and inter-letter spacing on letter-in-string identification

Effects of stimulus duration and inter-letter spacing were studied in a letter-in-string identification paradigm. Participants were shown strings of 5 random consonants (e.g., PGKDM) centered on fixation and were asked to identify the letter that had appeared at a post-cued location. Stimulus duration was manipulated in Experiment 1 (13 ms–91 ms), and inter-letter spacing manipulated in Experiment 2 (for a fixed stimulus duration of 26 ms). We contrasted performance to outer-letters (positions 1 and 5) with non-central inner letters (positions 2 and 4), the first-letter (position 1) with the final letter (position 5), and the central-letter (position 3) with the other inner letters (positions 2 and 4). The outer-letter advantage and the first-letter advantage were present throughout the entire range of exposure durations, whereas the central-letter advantage increased with longer exposures. On the other hand, increased spacing reduced both the outer-letter advantage and the first-letter advantage, whereas it led to a greater central-letter advantage. Changes in acuity and crowding as a function of stimulus exposure and inter-letter spacing, can account for this pattern of results.     

Effects of stimulus orientation on the identification of common polyoriented objects

Experimental evidence has shown that the time taken to recognize objects is often dependent on stimulus orientation in the image plane. This effect has been taken as evidence that recognition is mediated by orientation-specific stored representations of object shapes. However, the factors that determine the orientation specificity of these representations remain unclear. This issue is examined using a word-picture verification paradigm in which subjects identified line drawings of common mono- and polyoriented objects at different orientations. A detailed analysis of the results showed that, in contrast to mono-oriented objects, the recognition of polyoriented objects is not dependent on stimulus orientation. This interaction provides a further constraint on hypotheses about the factors that determine the apparent orientation specificity of stored shape representations. In particular, they support previous proposals that objects are encoded in stored representations at familiar stimulus orientations.     

Separate and shared sources of dual-task cost in stimulus identification and response selection

There is often strong interference if a second target stimulus (T2) is presented before processing of a prior target stimulus (T1) is complete. In the "Psychological Refractory Period" (PRP) paradigm, responses are speeded and interference manifests as increased response time for T2. In the "Attentional Blink" (AB) paradigm, stimuli are masked and responses unspeeded; interference manifests as reduced T2 accuracy. While different causes have usually been considered for PRP and AB phenomena, recent evidence has supported a unified account based on a single, shared restriction on concurrent processing. Here we show that a full assessment of separate and shared resource limitations requires direct comparison of hybrid PRP/AB trials with corresponding pure PRP and AB cases. Randomizing trial types in such a comparison also brings substantial benefit in addressing possible changes in task preparation or readiness. The data from two such experiments--combining speeded auditory (SA) and unspeeded visual (UV) task events--provide clear evidence for both separate and shared resource limitations. Often interference is strongest for T1 and T2 events of the same type, reflecting predominantly different limitations in SA and UV processing. With modest increases in demand, however, interference between different event types can also be made arbitrarily large, reflecting arbitrarily important shared limitations. For even such simple tasks as these, T--T2 interference reflects a combination of relatively local and relatively global sources.     

Information integration and the identification of stimulus noise and criterial noise in absolute judgment

Two main classes of theories have been proposed regarding range effects in unidimensional absolute-identification tasks. One class posits that as range is increased, criterial noise increases but stimulus noise remains constant. Another class posits increasing stimulus noise but constant criterial noise. In this study, an effort is made to help decide this issue. Multiple observations are used in several absolute-identification tasks of varying range. A stimulus integration model is proposed in which averaging takes place over stimulus internal representations, thereby reducing stimulus variance; on the other hand, it is assumed that criterial variance is unaffected by the number of observations. The model allows one to identify the relative amounts of stimulus noise and criterial noise inherent in observers' recognition judgments. The model yields good fits to data in several experiments, and it is concluded that both stimulus noise and criterial noise increase as range in the absolute-identification task is increased.     

Dissociating speed and accuracy in absolute identification: the effect of unequal stimulus spacing

Identification accuracy for sets of perceptually discriminable stimuli ordered on a single dimension (e.g., line length) is remarkably low, indicating a fundamental limit on information processing capacity. This surprising limit has naturally led to a focus on measuring and modeling choice probability in absolute identification research. We show that choice response time (RT) results can enrich our understanding of absolute identification by investigating dissociation between RT and accuracy as a function of stimulus spacing. The dissociation is predicted by the SAMBA model of absolute identification (Brown, Marley, Dockin, & Heathcote, 2008), but cannot easily be accommodated by other theories. We show that SAMBA provides an accurate, parameter free, account of the dissociation that emerges from the architecture of the model and the physical attributes of the stimuli, rather than through numerical adjustment. This violation of the pervasive monotonic relationship between RT and accuracy has implications for model development, which are discussed.

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Duration comparison: relative stimulus differences stimulus age, and stimulus predictiveness.

Under a psychophysical trials procedure, pigeons were presented with a red light of one duration followed by a green light of a second duration. Eight geometrically spaced base durations were paired with one of four shorter and four longer durations as the alternate member of a duration pair, with different pairs randomly intermixed. One choice was reinforced if red had lasted longer than green, and a second choice was reinforced if green had lasted longer. Performance was compared when all the base durations and their pair members were included (entire-range condition) or when only the four longest base durations and their comparison durations (restricted-range condition) were used. Discrimination sensitivity decreased for longer duration pairs under both conditions, supporting a memory-based account. Sensitivity was lower under the restricted-range condition. Under both conditions, a bias to report "green as longer" increased as the second green duration increased. Bias changed as a matching function of the green-duration predictiveness of the correct choice. The results are related to a quantitative model of timing and remembering proposed by Staddon.