Lateral masking as a function of spacing

It is argued that lateral masking is a composite of several processes. These processes include response competition, distribution of attention, perceptual grouping, and feature (contour) interaction. Three experiments were carried out in an attempt to isolate some of the components. In the first two experiments, it was shown that feature interaction dominates at close spacing but other processes dominate at wider spacing. The third experiment showed that at least part of the effect of perceptual grouping appears to be information provided about target location.     

Hemispheric asymmetries for global and local processing as a function of stimulus exposure duration

The experiments assess the relationship between stimulus exposure duration and hemispheric asymmetries for global and local processing. Six durations (27, 40, 53, 67, 80, and 147 ms) were tested in a selective attention task in which hierarchical letterforms were presented unilaterally to the left or right visual field. The results indicated that left hemisphere-local asymmetries were demonstrated more often than right hemisphere-global asymmetries and that asymmetries were most commonly found in the middle range of durations tested. The pattern of results emphasizes the importance of further study into those conditions under which the predicted asymmetries can be reliably demonstrated in healthy individuals.     

Buildup of proactive inhibition as a function of temporal spacing and adult age

Glenberg's theory of temporal distinctiveness (Glenberg, 1987; Glenberg & Swanson, 1986) was used to examine whether the buildup of proactive inhibition (PI) may be interpreted as an overloading of temporal retrieval cues. The Brown-Peterson task was selected on the basis of the assumption that successful performance on such a task requires the use of a recency rule where the subject must use temporal cues to retrieve the contents of the most recent study list. Two variables were manipulated that were presumed to affect the utilization of temporal cues: length of intertrial interval (ITI) (0 or 90 s) and adult age (young or elderly). Glenberg's theory suggests that temporal spacing improves memory by enhancing the distinctiveness of temporal retrieval cues. Thus, it was predicted that PI buildup should be less in the 90-s condition than in the 0-s condition. Assuming that older adults are more sensitive to the overloading of temporal cues, it was anticipated that older adults would experience a greater buildup of PI than younger adults at the 0-s condition. Results showed that although PI buildup varied with length of ITI, it did not vary with adult age. Analysis of delayed measures of recall, recognition, and temporal memory suggested that a retrieval interpretation based on Glenberg's theory is insufficient as an explanation of the current results; encoding difficulties also appear to contribute to the buildup of PI.     

Determinants of attention to local and global features of visual forms

This article deals with the problem of how attention is distributed to different levels of detail (global, local) in visual scenes. Six experiments explore the effect of a previous level of processing on current processing. The contention that processing at a given level of detail biases the distribution of attention so that more is allocated to that level for future processing is supported by the presence in the data of a robust level-readiness effect, whereby processing is faster at a given level if previous processing has been at that level. The level-readiness effect occurs regardless of the conspicuity of features at the various levels. Conflict between levels seems to depend on the imbalance of conspicuity and attention allocation between levels, with the more conspicuous or attended-to-level interfering more. A model of two-state attention switching similar to that of Sperling and Melchnor (1978) is proposed to explain these data. the final experiment confirmed the somewhat unusual prediction of this model that sometimes processing under focusing-attention conditions can be slower than that under divided-attention conditions.     

Haptic form perception: Relative salience of local and global features

John B. Pierce Laboratory and Yale University, New Haven, Connecticut When we examine objects haptically, do we weight their local and global features as we do visually, or do we place relatively greater emphasis on local shape? In Experiment 1, subjects made either haptic or visual comparisons of pairs of geometric objects (from a set of 16) differing in local and global shape. Relative to other objects, those with comparable global shape but different local features were judged less similar by touch than by vision. Separate groups of subjects explored the same objects while wearing either thick gloves (to discourage contour-following) or splinted gloves (to prevent enclosure). Ratings of similarity were comparable in these two conditions, suggesting that neither exploratory procedure was necessary, by itself, for the extraction of either local or global shape. In Experiment 2, haptic exploration time was restricted to 1, 4, 8, or 16 sec. Limiting exploration time affected relative similarity in objects differing in their local but not their global shape. Together, the findings indicate that the haptic system initially weights local features more heavily than global ones, that this differential weighting decreases over time, and that neither contour-following nor enclosure is exclusively associated with the differential emphasis on local versus global features.     

The perception of multiple simultaneously presented forms as a function of foveal spacing

Using five capital letters as the form stimuli and tachistoscopic presentation, an exposure duration was determined for each S that yielded 80% identification accuracy when single letter displays were presented. Then the increment in exposure duration necessary for a correct identification of all letters on a display on 80% of the trials was determined for 2, 3, and 4 letter displays. In view of evidence that perceptual independence breaks down when stimuli are spaced much closer than 1° apart in the fovea, the effect of different foveal spacing of the form stimuli in the display was studied. Spacings of 1/2, 3/4, and 1° of angle were employed. Less than a 30% increment in exposure duration was necessary to recognize 2 form displays at the same accuracy level as single form. But no further increase in exposure duration was necessary to recognize 3 and 4 form displays at the same accuracy criterion. Evidence for positive correlation of sensory perceptual error for forms spaced less than 1° apart in the fovea was found.     

Haptic form perception: relative salience of local and global features.

When we examine objects haptically, do we weight their local and global features as we do visually, or do we place relatively greater emphasis on local shape? In Experiment 1, subjects made either haptic or visual comparisons of pairs of geometric objects (from a set of 16) differing in local and global shape. Relative to other objects, those with comparable global shape but different local features were judged less similar by touch than by vision. Separate groups of subjects explored the same objects while wearing either thick gloves (to discourage contour-following) or splinted gloves (to prevent enclosure). Ratings of similarity were comparable in these two conditions, suggesting that neither exploratory procedure was necessary, by itself, for the extraction of either local or global shape. In Experiment 2, haptic exploration time was restricted to 1, 4, 8, or 16 sec. Limiting exploration time affected relative similarity in objects differing in their local but not their global shape. Together, the findings indicate that the hepatic system initially weights local features more heavily than global ones, that this differential weighting decreases over time, and that neither contour-following nor enclosure is exclusively associated with the differential emphasis on local versus global features.     

Visual search for global/local stimulus features in humans and baboons

Fagot and Deruelle (1997) demonstrated that, when tested with identical visual stimuli, baboons exhibit an advantage in processing local features, whereas humans show the “global precedence” effect initially reported by Navon (1977). In the present experiments, we investigated the cause of this species difference. Humans and baboons performed a visual search task in which the target differed from the distractors at either the global or the local level. Humans responded more quickly to global than to local targets, whereas baboons did the opposite (Experiment 1). Human response times (RTs) were independent of display size, for both local and global processing. Baboon RTs increased linearly with display size, more so for global than for local processing. The search slope for baboons disappeared for continuous targets (Experiment 2). That effect was not due to variations in stimulus luminance (Experiment 3). Finally, variations in stimulus density affected global search slopes in baboons but not in humans (Experiment 4). Overall, results suggest that perceptual grouping operations involved during the processing of hierarchical stimuli are attention demanding for baboons, but not for humans.     

Managing two cultural identities: the malleability of bicultural identity integration as a function of induced global or local processing

Increasingly, individuals identify with two or more cultures. Prior research has found the degree to which individuals chronically integrate these identities (bicultural identity integration; BII) moderates responses to cultural cues: High BII individuals assimilate (adopting biases that are congruent with norms of the cued culture), whereas low BII individuals contrast (adopting biases that are incongruent with these norms). The authors propose BII can also be a psychological state and modulated by shifts in processing styles. In four experiments, the authors induced a global or local processing style using physical posture (Experiment 1) and cognitive manipulations (Experiments 2-4) and found that BII is enhanced in contexts facilitating a more global processing style (i.e., smiling, high-level construal, and similarity focus). The authors also found that contrastive responses to cultural cues are diminished when BII is situationally enhanced. Implications for research on processing style, identity integration, and performance in culture-based situations are discussed.     

A functional near-infrared spectroscopy study of sustained attention to local and global target features

Despite a long history of vigilance research, the role of global and local feature discrimination in vigilance tasks has been relatively neglected. In this experiment participants performed a sustained attention task requiring either global or local shape stimuli discrimination. Reaction time to local feature discriminations was characterized by a quadratic trend over time-on-task with performance levels returning to initial levels late in the task. This trend did not occur in the global shape discrimination task. Functional near-infrared spectroscopy (fNIRS) was utilized in this study as an index of cerebral activation. In both tasks there was increased right hemisphere relative to left hemisphere oxygenation and right hemisphere oxygenation increased with time-on-task. Left hemisphere oxygenation, however, decreased slightly in the global task, but increased significantly in the local task as task duration increased. Indeed, total oxygenation, averaging both right and left, increased more with time-on-task in the local discrimination task. Both the performance and physiological results of this study indicate increased utilization of bilateral cerebral resources with time-on-task in the local, but not the global discrimination vigil.     

Choice as a function of local versus molar reinforcement contingencies.

Rats were trained on a discrete-trial probability learning task. In Experiment 1, the molar reinforcement probabilities for the two response alternatives were equal, and the local contingencies of reinforcement differentially reinforced a win-stay, lose-shift response pattern. The win-stay portion was learned substantially more easily and appeared from the outset of training, suggesting that its occurrence did not depend upon discrimination of the local contingencies but rather only upon simple strengthening effects of individual reinforcements. Control by both types of local contingencies decreased with increases in the intertrial interval, although some control remained with intertrial intervals as long as 30 s. In Experiment 2, the local contingencies always favored win-shift and lose-shift response patterns but were asymmetrical for the two responses, causing the molar reinforcement rates for the two responses to differ. Some learning of the alternation pattern occurred with short intertrial intervals, although win-stay behavior occurred for some subjects. The local reinforcement contingencies were discriminated poorly with longer intertrial intervals. In the absence of control by the local contingencies, choice proportion was determined by the molar contingencies, as indicated by high exponent values for the generalized matching law with long intertrial intervals, and lower values with short intertrial intervals. The results show that when molar contingencies of reinforcement and local contingencies are in opposition, both may have independent roles. Control by molar contingencies cannot generally be explained by local contingencies.     

Attention and size in a global/local task

Two-letter stimuli, consisting of one small letter inside a much larger one (in Experiments 1A, 1B, and 2) or inside a "blob" (in Experiment 3), were used to examine the role of size difference in global/local tasks. The small letter was placed at locations that avoided contour interactions. The results showed no identity interference, in that the specific identity of the large letter did not differentially affect identification of the small one. However, there was evidence of global advantage, in that the presence of a large letter hindered identification of the small one. The magnitude of the global advantage effect, as measured by the difference in performance between the small-single and small-embedded conditions, was largest (about 200 ms reaction time (RT) difference) when the large letters were the same as the small ones, lower (a 63 ms difference in Experiment IB, and 89 ms in Experiment 2) when the large letters were unrelated to the small ones, and lowest (a 25 ms difference) when the large stimuli were blobs. It is proposed that the amount of interference depends on the overlap between the features of the large stimuli, as a set, and those of the small ones, also as a set.     

Sustained attention to local and global target features is different: Performance and tympanic membrane temperature

Vision researchers have investigated the differences between global and local feature perception. No one has, however, examined the role of global and local feature discrimination in sustained attention tasks. In this experiment participants performed a sustained attention task requiring either global or local letter target discriminations or watched the same displays without any work imperative. Reaction time to targets was slower when global feature discriminations were required than when local feature discriminations were required. Tympanic membrane temperature (TMT) was utilized in this study as an index of cerebral activation. Participants in the global letter detection condition had elevated post-task right TMT, indicative of reduced cerebral activation in the right hemisphere, in comparison to participants in the local letter detection or no-work imperative conditions. Both the performance and physiological results of this study indicate increased cognitive fatigue when global feature discriminations are required.     

Simultaneous encoding of direction at a local and global scale

Human observers can simultaneously encode direction information at two different scales, one local (an individual dot) and one global (the coherent motion of a field of dots distrisbuted over a 10°-diameter display). We assessed whether encoding global motion would preclude the encoding of a local trajectory component and vice versa. In the present experiments, a large number (100–150) of dots were randomly assigned directions in each frame from a uniform distribution of directions spanning a range of 160° to create global motion in a single direction (Williams & Sekuler, 1984). Amidst these background dots, 1 dot moved in a consistent direction (trajectory) for the duration of the display. The direction of this “trajectory dot” was similar to the mean direction of the distribution of directions determining the movement of the background dots. Direction discrimination for both the global motion and the trajectory was measured, using the method of constant stimuli, under precued and postcued partial report conditions. A low- or high-frequency 85-msec tone signaled which motion the subject was to judge. In the precue condition, the tone was presented 200 msecbefore the onset of the stimulus, whereas in the postcue condition, the tone was presented immediatelyafter the offset of the stimulus. Direction discrimination thresholds for both global and local motion in the postcued condition were not significantly different from those obtained in the precued condition. These results suggest that direction information for both global and local motion is encoded simultaneously and that the observer has access to either motion signal after the presentation of a stimulus.