Attention: Reaction Time and Accuracy Reveal Different Mechanisms.

The authors propose that there are 2 different mechanisms whereby spatial cues capture attention. The voluntary mechanism is the strategic allocation of perceptual resources to the location most likely to contain the target. The involuntary mechanism is a reflexive orienting response that occurs even when the spatial cue does not indicate the probable target location. Voluntary attention enhances the perceptual representation of the stimulus in the cued location relative to other locations. Hence, voluntary attention affects performance in experiments designed around both accuracy and reaction time. Involuntary attention affects a decision as to which location should be responded to. Because involuntary attention does not change the perceptual representation, it affects performance in reaction time experiments but not accuracy experiments. The authors obtained this pattern of results in 4 different versions of the spatial cuing paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does attention affect visual feature integration?

Investigated whether (1) the integration of color and shape information is affected by attending to the stimulus location and (2) attending to a stimulus location enhances the perceptual representation of the stimulus or merely affects decision processes. In 3 experiments with 39 Ss (aged 16–38 yrs), Ss were briefly presented with colored letters. On most trials, Ss were precued to the stimulus location (valid cue); on some trials, a nonstimulus location was cued (invalid cue). Ss were less likely to combine colors and letter shapes incorrectly following a valid cue. The attentional facilitation afforded by the cue was not limited to feature integration but also affected the registration of features; however, when the amount of feature information was strictly controlled, attention still affected feature integration. It is suggested that orienting attention to the location of the cue affects the quality of the perceptual representation for features and their integration. (31 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Loosening the constraints on illusory conjunctions: Assessing the roles of exposure duration and attention.

Illusory conjunctions are the incorrect combination of correctly perceived features, such as color and shape. They have been found to occur using a brief exposure (under 200 msec) and a dual task designed to divert attention. The present study investigated the roles of exposure duration and attention in obtaining illusory conjunctions. Several mathematical models of the feature integration task were also assessed. Exp 1 tested participants' accuracy at combining features using a long exposure and an attention-diverting task. Exp 2 compared performance with and without the attention-diverting task. The final experiment compared performance using a brief (0.15 sec) and a long (1.5 sec) exposure duration without an attention-diverting task. Neither attention nor exposure duration had a significant effect on feature integration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Illusory conjunctions are alive and well: A reply to Donk (1999).

When presented with a red T and a green O, observers occasionally make conjunction responses and indicate that they saw a green T. These errors have been interpreted as reflecting separable processing stages of feature detection and integration with the illusory conjunctions arising from a failure at the integration stage. Recently, M. Donk (see record 1999-11444-003) asserted that the phenomenon of illusory conjunctions is an artifact. Conjunction reports are actually the result of confusing a nontarget item (O in the example above) for a target item (the letter T) and (correctly) reporting the color associated with the (incorrectly) selected target. The authors demonstrate that although target–nontarget confusion errors are a potential source of conjunction reports, there is a plethora of findings that cannot be accounted for by this confusion model. A review of the literature indicates that in many studies, illusory conjunctions do result from a failure to properly integrate features. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of attention on phenomenal length

Family history of atherosclerosis has been recognised as an nonmodifiable cardiovascular risk factor. Lipid levels, together with hypertension and diabetes, appear to have an inheritable component. The aim of the study was to ascertain whether lipoprotein abnormalities of 169 adult patients with non-coronary atherosclerosis were associated with a family history of atherosclerosis. Besides intermediate density lipopoprotein composition and Lp(a) levels, we focused on apo(a) and apo E phenotypes, LDL cholesterol/apo B ratio, VLDL triglyceride/HDL cholesterol ratio, and environmental factors. We found that patients with a family history of atherosclerosis had a higher prevalence of VLDL triglyceride/HDL cholesterol ratio above 1.8 (51.3% vs 34.7%) than patients without. Similarly, there was a significant inverse correlation between both considered ratios (r = -0.24, p < 0.05). The odds ratio of the presence of both abnormal ratios (4.60, 95% CI, 1.41-15.00) and low molecular weight apo(a) isoforms (3.30, 95% CI, 1.05-10.30 and family history of atherosclerosis was independent of smoking and hypertension. Apo(a) isoform size seems to be more important than Lp(a) concentrations in the family history of atherosclerosis risk determination. Subsequent analysis showed that patients with a family history of atherosclerosis had a greater-than-fourfold increased risk of having one or both abnormal ratios reflecting metabolic disturbances which probably constitute a combined trait. Family history of atherosclerosis may constitute a specific lipoprotein-related marker of atherosclerosis. Such a marker often precedes the onset of overt disease and may contribute to identifying patients with an atherogenic lipoprotein profile even in the absence of classical lipid risk factors.     

If it's not there, where is it? Locating illusory conjunctions.

There is evidence that complex objects are decomposed by the visual system into features, such as shape and color. Consistent with this theory is the phenomenon of illusory conjunctions, which occur when features are incorrectly combined to form an illusory object. We analyzed the perceived location of illusory conjunctions to study the roles of color and shape in the location of visual objects. In Experiments 1 and 2, participants located illusory conjunctions about halfway between the veridical locations of the component features. Experiment 3 showed that the distribution of perceived locations was not the mixture of two distributions centered at the 2 feature locations. Experiment 4 replicated these results with an identification task rather than a detection task. We concluded that the locations of illusory conjunctions were not arbitrary but were determined by both constituent shape and color. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neon colors illuminate reading units.

The effect of syllable-size reading units on neon color was investigated in 6 experiments. The stimuli consisted of 5- or 7-letter words or pseudowords with a syllable break either just before or just after the middle (target) letter. The target letter was overlaid with a plaid of red and green lines that gave it an ambiguous neon color. The letters preceding the target were overlaid with a monochromatic grid (red or green), and the letters following the target were overlaid with the other color. Ss were significantly more likely to judge the target as more similar to the color of other letters within its syllable than colors of letters outside that unit. The effect was shown not to be an artifact of guessing strategy or eye movements. Word structure determined by orthography and morphology affected neon colors, but no effect was found for purely phonological units. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional theory of illusory conjunctions and neon colors.

Illusory conjunctions are the incorrect perceptual combination of briefly presented colors and shapes. In the neon colors illusion, achromatic figures take on the color of an overlaid grid of colored lines. Both illusions are explained by a theory that assumes (a) poor location information or poor spatial resolution for some aspects of visual information and (b) that the spatial location of features is constrained by perceptual organization. Computer simulations demonstrate that the mechanisms suggested by the theory are useful in veridical perception and they are sufficient to produce illusory conjunctions. The theory suggests mechanisms that economically encode visual information in a way that filters noise and fills in missing data. Issues related to neural implementation are discussed. Four experiments illustrate the theory. Illusory conjunctions are shown to be affected by objective stimulus organization, by subjective organization, and by the linguistic structure of ambiguous Hebrew words. Neon colors are constrained by linguistic structure in the same way as illusory conjunctions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A measurement theory of illusory conjunctions.

Illusory conjunctions refer to the incorrect perceptual combination of correctly perceived features, such as color and shape. Research on the phenomenon has been hampered by the lack of a measurement theory that accounts for guessing features, as well as the incorrect combination of correctly perceived features. Recently, several investigators have suggested using multinomial models as a tool for measuring feature integration. The authors examined the adequacy of these models in 2 experiments by testing whether model parameters reflect changes in stimulus factors. In a third experiment, confidence ratings were used as a tool for testing the model. Multinomial models accurately reflected both variations in stimulus factors and observers' trial-by-trial confidence ratings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Phenomenology of attention: I. Color, location, orientation, and spatial frequency.

The effect of attention on the phenomenal appearance of objects was investigated in the domains of color (hue), location, line orientation, and spatial frequency. Observers indicated the appearance of a briefly presented above-threshold stimulus by selecting a matching stimulus along a sensory continuum (e.g., color). Attention was manipulated with a dual task that involved letter identification. Attention had little effect in changing the way objects appeared in terms of observers' mean response. However, in each stimulus domain, attention reduced the variability of responses. It is argued that attention should be viewed in terms of reducing uncertainty. (PsycINFO Database Record (c) 2010 APA, all rights reserved)