The identity intrusion effect: Attentional capture or perceptual load?

Effects of working memory contents and perceptual load on distractor processing: When a response-related distractor is held in working memory

Working memory and attention are closely related. Recent research has shown that working memory can be viewed as internally directed attention. Working memory can affect attention in at least two ways. One is the effect of working memory load on attention, and the other is the effect of working memory contents on attention. In the present study, an interaction between working memory contents and perceptual load in distractor processing was investigated. Participants performed a perceptual load task in a standard form in one condition (Single task). In the other condition, a response-related distractor was maintained in working memory, rather than presented in the same stimulus display as a target (Dual task). For the Dual task condition, a significant compatibility effect was found under high perceptual load; however, there was no compatibility effect under low perceptual load. These results suggest that the way the contents of working memory affect visual search depends on perceptual load.

Interactions Between Modality of Working Memory Load and Perceptual Load in Distractor Processing

The present study investigated interactions between working memory load and perceptual load. The load theory (Lavie, Hirst, de Fockert, & Viding, 2004 ) claims that perceptual load decreases distractor interference, whereas working memory load increases interference. However, recent studies showed that effects of working memory might depend on the relationship between modalities of working memory and task stimuli. Here, we examined whether the relationship between working memory load and perceptual load would remain the same across modalities. The results of Experiment 1 showed that verbal working memory load did not affect a compatibility effect for low perceptual load, whereas it increased the compatibility effect for high perceptual load. In Experiment 2, the compatibility effect remained the same regardless of visual working memory load. These results suggest that the effects of working memory load and perceptual load depend on the relationship between the modalities of working memory and stimuli.

On the limits of top-down control of visual selection

In the present study, observers viewed displays in which two equally salient color singletons were simultaneously present. Before each trial, observers received a word cue (e.g., the word red, or green) or a symbolic cue (a circle colored red or green) telling them which color singleton to select on the upcoming trial. Even though many theories of visual search predict that observers should be able to selectively attend the target color singleton, the results of the present study show that observers could not select the target singleton without interference from the irrelevant color singleton. The results indicate that the irrelevant color singleton captured attention. Only when the color of the target singleton remained the same from one trial to the next was selection perfect—an effect that is thought to be the result of passive automatic intertrial priming. The results of the present study demonstrate the limits of top-down attentional control.

Attentional capture by motion onsets is modulated by perceptual load

The onset of motion captures attention during visual search even if the motion is not task relevant, which suggests that motion onsets capture attention in a stimulus-driven manner. However, we have recently shown that stimulus-driven attentional capture by abruptly appearing objects is attenuated under conditions of high perceptual load. In the present study, we examined the influence of perceptual load on attentional capture by another type of dynamic stimulus: the onset of motion. Participants searched for a target letter through briefly presented low- and high-load displays. On each trial, two irrelevant flankers also appeared, one with a motion onset and one that was static. Flankers defined by a motion onset captured attention in the low-load but not in the high-load displays. This modulation of capture in high-load displays was not the result of overall lengthening of reaction times (RTs) in this condition, since search for a single low-contrast target lengthened RTs but did not influence capture. These results, together with those of previous studies, suggest that perceptual load can modulate attentional capture by dynamic stimuli.

Top-down and bottom-up control of visual selection

The present paper argues for the notion that when attention is spread across the visual field in the first sweep of information through the brain visual selection is completely stimulus-driven. Only later in time, through recurrent feedback processing, volitional control based on expectancy and goal set will bias visual selection in a top-down manner. Here we review behavioral evidence as well as evidence from ERP, fMRI, TMS and single cell recording consistent with stimulus-driven selection. Alternative viewpoints that assume a large role for top-down processing are discussed. It is argued that in most cases evidence supporting top-down control on visual selection in fact demonstrates top-down control on processes occurring later in time, following initial selection. We conclude that top-down knowledge regarding non-spatial features of the objects cannot alter the initial selection priority. Only by adjusting the size of the attentional window, the initial sweep of information through the brain may be altered in a top-down way.