Object-based attentional selection and aging

The authors conducted 2 studies to examine potential age-related differences in object-based attentional selection. Participants were briefly presented with pairs of wrenches and were asked to make 1 response if both target properties (i.e., an open end and a hexagonal end) were present and another response if only a single target property was present in the display. The critical manipulation was whether the target properties were present on 1 wrench or distributed between 2 wrenches. Space-based models of selective attention predict no difference in performance between these conditions. However, object-based attentional selection models predict better performance when both target properties appear on a single object. The results from both of the studies were consistent with object-based models of attentional selection. Furthermore, both young and old adults showed similar performance effects, suggesting the object-based attentional selection is insensitive to normal aging.     

Object-based attentional selection and awareness of objects

This study examined whether object-based attentional selection depends on the observer's awareness of objects, using objects defined by perceptual completion. As an indicator of object-based attention, we studied the same-object advantage, where observers respond faster to a target within a cued object than within a noncued object. The same-object advantage was not found in the condition where observers were unaware of the objects (inattentional blindness). On the other hand, the same-object advantage was observed in the condition where observers were aware of the objects. These results suggest that the intensity of object representations can be influenced by observers’ awareness of objects, which affects the occurrence of object-based effects. We propose that attention/inattention (or awareness/unawareness) is graded and observers’ awareness of the objects might serve to boost an otherwise noisy/low signal representation for obtaining object-based effects.     

Object-based selection: the role of attentional shifts

The objective of this paper was to investigate under what conditions object-based effects are observed. Recently, Watson and Kramer (1999) used a divided-attention task and showed that unless top-down factors induce a bias toward selection at a higher level, object-based effects are obtained when same-object targets belong to the same uniformly connected (single-UC) region, but not when they belong to different single-UC regions grouped into a higher order object (grouped-UC regions). We refine this claim by proposing that a critical factor in determining whether or not object-based effects with grouped-UC regions are observed is the need to shift attention. The results of four experiments support this hypothesis. Stimuli and displays were similar to those used by Egly, Driver, and Rafal (1994). Subjects had to make size judgments. Using different paradigms, we obtained object-based effects when the task required shifts of attention (spatial cuing, same vs. different judgment with asynchronous target onsets), but not when attention remained either broadly distributed (same vs. different judgment with simultaneous targets) or tightly focused (response competition paradigm).     

Goal-referenced selection of verbal action: modeling attentional control in the Stroop task

This article presents a new account of the color-word Stroop phenomenon (J. R. Stroop, 1935) based on an implemented model of word production, WEAVER++ (W. J. M. Levelt, A. Roelofs, & A. S. Meyer, 1999b; A. Roelofs, 1992, 1997c). Stroop effects are claimed to arise from processing interactions within the language-production architecture and explicit goal-referenced control. WEAVER++ successfully simulates 16 classic data sets, mostly taken from the review by C. M. MacLeod (1991), including incongruency, congruency, reverse-Stroop, response-set, semantic-gradient, time-course, stimulus, spatial, multiple-task, manual, bilingual, training, age, and pathological effects. Three new experiments tested the account against alternative explanations. It is shown that WEAVER++ offers a more satisfactory account of the data than other models.     

Depth cues do not underlie attentional modulations of the Stroop effect

The well-known Stroop effect is usually attributed to the automaticity of word reading. Recently, Wühr and Waszak (2003) had participants name the color of one of two rectangles and found that words in the relevant object produced larger Stroop effects than did words in the irrelevant object or in the background. They attributed this difference to an object-based mechanism of attentional selection that amplifies processing of all the features of an attended object. However, in the displays used by Wühr and Waszak, occlusion suggested the presence of different depth planes. Hence, the increased Stroop effect could have resulted from perceiving the words to be in the same depth plane as the relevant object and not from perceiving the words to be parts of the relevant object. Two experiments tested between these accounts by using displays without monocular depth cues. The results of both experiments replicate those of Wühr and Waszak, supporting their object-based account.     

Object-based selection in the Baylis and Driver (1993) paradigm is subject to space-based attentional modulation

Three experiments re-examined Baylis and Driver's (1993) strong evidence for object-based selection, that making relative apex location judgments is harder between two objects than within a single object, with object (figure-ground) segmentation determined solely by color-based perceptual set. Using variations of the Baylis and Driver paradigm, the experiments replicated a two-object cost. However, they also showed a large part of the two-object cost to be attributable to space-based factors, though there remained an irreducible cost consistent with 'true' object-based selection.     

Actions modulate attentional capture

The purpose of the present study was to determine whether the action system plays a role in determining which stimulus characteristics capture attention by assessing the interference effects caused by dynamic discontinuities that have similar attention-capturing properties, but different action affordances. Results revealed that offset distractors caused significant interference when onset targets were presented in a keypress task, but did not increase reaction times when the same onset targets were presented in a goal-directed aiming task In contrast, onset distractors caused interference when offset targets were presented in both keypress and aiming tasks. This pattern of results suggests that the attentional set, and thus the properties of stimuli that capture attention, is modulated by the interaction between stimulus and response expectations.     

Actions modulate attentional capture

The purpose of the present study was to determine whether the action system plays a role in determining which stimulus characteristics capture attention by assessing the interference effects caused by dynamic discontinuities that have similar attention-capturing properties, but different action affordances. Results revealed that offset distractors caused significant interference when onset targets were presented in a keypress task, but did not increase reaction times when the same onset targets were presented in a goal-directed aiming task. In contrast, onset distractors caused interference when offset targets were presented in both keypress and aiming tasks. This pattern of results suggests that the attentional set, and thus the properties of stimuli that capture attention, is modulated by the interaction between stimulus and response expectations.     

Seeing while acting: hand movements can modulate attentional capture by motion onset

The onset of new motion has been shown to be a very robust cause of attentional capture, generating a processing advantage for the location of motion onset regardless of the observer's concurrent goal. The present study, motivated by the common-coding account of action and perception, examined whether the effect of motion onset on visual attention can be modulated by the observer's mode of action. Specifically, the common-coding account predicts that preparing an action can render the features that are used in the action plan less available for visual processes. Consistent with this hypothesis, in Experiment 1 the magnitude of attentional capture caused by a single motion onset was reduced when this motion was similar to the observer's response (i.e., along the same axis). Similarly, in Experiment 2 the onset of a response-different motion gained a processing advantage over the response-similar motion onset when the two were presented simultaneously. Since both types of motion were present in every trial, the results of Experiment 2 suggest that response similarity affected visual-attentional processes rather than motor processes. Together, these results suggest that the processes of attentional prioritization caused by motion onset can be modulated by the observer's concurrent action.     

Independent race of colour and word can predict the Stroop effect

Mainstream theories of the Stroop effect suggest that faster colour classification on congruent trials (say, the word RED printed in red colour) relative to incongruent trials (GREEN in red) is due to channel interaction. Namely, information from the irrelevant word channel perturbs processing of the print colour, causing in turn slower processing of incongruent displays. In this note, I advance a new model in which colour and word are processed in parallel and completely independent channels. The Stroop effect is then the outcome of signal redundancy in congruent displays, where both colour and word contribute to the same response. Numerical computations show that the model can produce the Stroop effect (along with high accuracy rates) for a subset of parameter values. Thus, it provides a proof of existence for a separate channel theory, and a challenge to many existing theories.     

Temporal expectations modulate attentional capture

Subjects’ ability to override attentional capture by salient distractors during singleton search has been attributed to the adoption of an attentional set for the type of discontinuity characterizing the target (Folk, Remington, & Johnston, 1992) or to fast disengagement of attention from the salient distractor’s location (Theeuwes, Atchley, & Kramer, 2000). The present results support an alternative account by showing that temporal expectancies modulate attentional capture. In a color singleton search, an irrelevant onset preceding the target by a given time interval produced capture when the distractor-to-target interval varied unpredictably but failed to do so when this interval was predictable. Moreover, with unpredictable intervals and moderately salient stimuli, capture was overridden at the expected average interval. These findings invite caution when stimulus onset asynchrony manipulations are used to study the temporal deployment of attention, since they demonstrate that such manipulations introduce powerful temporal expectations.     

The role of attentional slippage in Stroop dilution

The present study examined the cognitive locus of Stroop dilution using a psychological refractory period (PRP) paradigm. Participants were asked to perform a tone discrimination task via a bimanual keypress response and a modified Stroop task via a vocal response serially as Task 1 and Task 2, respectively. In Task 2, a neutral word was added on half of the trials and no neutral word on the other half of the trials to observe the Stroop dilution effect. The amount of Stroop dilution, as well as the Stroop effect, was relatively constant across different stimulus-onset asynchronies (SOAs), which implies that Stroop dilution occurs due to the competition between a neutral word and a color word after a target color bar is selected to be processed further. These results indicate that focused attention plays an important role in the modulation of Stroop interference by the presence of a neutral word.     

Object-based attentional effects in response to eye-gaze and arrow cues

Recent studies have demonstrated that central cues, such as eyes and arrows, reflexively trigger attentional shifts. However, it is not clear whether the attention induced by these two cues can be attached to objects within the visual scene. In the current study, subjects' attention was directed to one of two objects (square outlines) via the observation of uninformative directional arrows or eye gaze. Then, the objects rotated 90° clockwise or counter-clockwise to a new location and the target stimulus was presented within one of these two objects. Results showed that independent of the cue type participants responded faster to targets in the cued object than to those in the uncued object. This suggests that in dynamic displays, both gaze and arrow cues are able to trigger reflexive shifts of attention to objects moving within the visual scene.     

Object-based attention: strength of object representation and attentional guidance

Two or more features belonging to a single object are identified more quickly and more accurately than are features belonging to different objects--a finding attributed to sensory enhancement of all features belonging to an attended or selected object. However, several recent studies have suggested that this "single-object advantage" may be a product of probabilistic and configural strategic prioritizations rather than of object-based perceptual enhancement per se, challenging the underlying mechanism that is thought to give rise to object-based attention. In the present article, we further explore constraints on the mechanisms of object-based selection by examining the contribution of the strength of object representations to the single-object advantage. We manipulated factors such as exposure duration (i.e., preview time) and salience of configuration (i.e., objects). Varying preview time changes the magnitude of the object-based effect, so that if there is ample time to establish an object representation (i.e., preview time of 1,000 msec), then both probability and configuration (i.e., objects) guide attentional selection. If, however, insufficient time is provided to establish a robust object-based representation, then only probabilities guide attentional selection. Interestingly, at a short preview time of 200 msec, when the two objects were sufficiently different from each other (i.e., different colors), both configuration and probability guided attention selection. These results suggest that object-based effects can be explained both in terms of strength of object representations (established at longer exposure durations and by pictorial cues) and probabilistic contingencies in the visual environment.     

Object-based attention overrides perceptual load to modulate visual distraction

The ability to ignore task-irrelevant information and overcome distraction is central to our ability to efficiently carry out a number of tasks. One factor shown to strongly influence distraction is the perceptual load of the task being performed; as the perceptual load of task-relevant information processing increases, the likelihood that task-irrelevant information will be processed and interfere with task performance decreases. However, it has also been demonstrated that other attentional factors play an important role in whether or not distracting information affects performance. Specifically, object-based attention can modulate the extent of distractor processing, leaving open the possibility that object-based attention mechanisms may directly modulate the way in which perceptual load affects distractor processing. Here, we show that object-based attention dominates perceptual load to determine the extent of task-irrelevant information processing, with distractors affecting performance only when they are contained within the same object as the task-relevant search display. These results suggest that object-based attention effects play a central role in selective attention regardless of the perceptual load of the task being performed.     

Hypnotic susceptibility, baseline attentional functioning, and the Stroop task

According to the theoretical framework relating hypnosis to attention, baseline attentional functioning in highly hypnotizable individuals should be more efficient than in low hypnotizable individuals. However, previous studies did not find differences in Stroop-like tasks in which the measure indicative of the Stroop interference effect was based on response latencies. This study was designed to determine whether subjects with different levels of hypnotic susceptibility show differences in baseline attentional functioning. To assess this hypothesis, high, medium, and low hypnotizable subjects performed a Stroop task designed to evaluate accuracy performance, before being subjected to hypnotic induction. Results showed that the Stroop interference effect was smaller in high hypnotizable subjects than in low hypnotizable subjects, whereas it was not different between high, and medium hypnotizable subjects. This outcome supports the notion that baseline attentional functioning is related to hypnotic susceptibility.     

When the visual format of the color carrier word does and does not modulate the Stroop effect

We investigated the impact of making the color carrier word visually unfamiliar via case and font mixInG in the context of three Stroop experiments. Experiment 1 yielded an increase in the size of the Stroop effect when the color carrier words were visually unfamiliar relative to lowercase words that were case and font consistent. Experiments 2A and 2B showed that the modulation of the Stroop effect by visual familiarity observed in Experiment 1 was eliminated when there was no correlation between the color and the color carrier word. These results are considered in the light of four different theoretical accounts of the Stroop effect (strength of association [Cohen, Dunbar, & McClelland, 19901, instance [Logan, 1988], schema [MacLeod, 2000], and obligatory processing followed by deactivation [Coltheart, Woollams, Kinoshita, & Perry, 1999]). None of these accounts appear capable of explaining all the results.     

Working memory demands modulate cognitive control in the Stroop paradigm

One important task of cognitive control is to regulate behavior by resolving information processing conflicts. In the Stroop task, e.g., incongruent trials lead to conflict-related enhancements of cognitive control and to improved behavioral performance in subsequent trials. Several studies suggested that these cognitive control processes are functionally and anatomically related to working memory (WM) functions. The present study investigated this suggestion and tested whether these control processes are modulated by concurrent WM demands. For this purpose, we performed three experiments in which we combined different WM tasks with the Stroop paradigm and measured their effects on cognitive control. We found that high WM demands led to a suppression of conflict-triggered cognitive control, whereas our findings suggest that this suppression effect is rather due to WM updating than to maintenance demands. We explain our findings by assuming that WM processes interfere with conflict-triggered cognitive control, harming the efficiency of these control processes.     

Object-based anisotropies in the flash-lag effect

The relative visual position of a briefly flashed stimulus is systematically modified in the presence of motion signals. We investigated the two-dimensional distortion of the positional representation of a flash relative to a moving stimulus. Analysis of the spatial pattern of mislocalization revealed that the perceived position of a flash was not uniformly displaced, but instead shifted toward a single point of convergence that followed the moving object from behind at a fixed distance. Although the absolute magnitude of mislocalization increased with motion speed, the convergence point remained unaffected. The motion modified the perceived position of a flash, but had little influence on the perceived shape of a spatially extended flash stimulus. These results demonstrate that motion anisotropically distorts positional representation after the shapes of objects are represented. Furthermore, the results imply that the flash-lag effect may be considered a special case of two-dimensional anisotropic distortion.