Set-size effects in simple visual search for contour curvature

In a visual-search paradigm, both perception and decision processes contribute to the set-size effects. Using yes - no search tasks in set sizes from 2 to 8 for contour curvature, we examined whether the set-size effects are predicted by either the limited-capacity model or the decision-noise model. There are limitations in perception and decision-making in the limited-capacity model, but only in decision-making in the decision-noise model. The results of four experiments showed that the slopes of the logarithm of threshold plotted against the logarithm of set size ranged from 0.24 to 0.32, when the curvature was high or low, contour convexity was upward or downward, and stimulus was masked or unmasked. These slopes were closer to the prediction of 0.23 by the decision-noise model than that of 0.73 by the limited-capacity model. We interpret this that in simple visual search for contour curvature, the decision noise mainly affects the set-size effects and perceptual capacity is not limited.     

Predictive and postdictive mechanisms jointly contribute to visual awareness

One of the fundamental issues in visual awareness is how we are able to perceive the scene in front of our eyes on time despite the delay in processing visual information. The prediction theory postulates that our visual system predicts the future to compensate for such delays. On the other hand, the postdiction theory postulates that our visual awareness is inevitably a delayed product. In the present study we used flash-lag paradigms in motion and color domains and examined how the perception of visual information at the time of flash is influenced by prior and subsequent visual events. We found that both types of event additively influence the perception of the present visual image, suggesting that our visual awareness results from joint contribution of predictive and postdictive mechanisms.     

Attentional bias to direct gaze in a dot-probe paradigm

Previous research has suggested that a singly presented facial stimulus having a direct gaze holds spatial attention. This study examined whether facial stimulus having a direct gaze can also capture spatial attention in a relative dot-probe paradigm (facial stimulus having a direct gaze was presented concurrently with that having an averted gaze). The results showed that participants oriented their spatial attention to a facial stimulus having a direct gaze rather than to that with an averted gaze. This attentional bias depended on gaze-perception mechanisms as observed in the lack of attentional bias to a direct gaze from unnatural-looking eyes (i.e., white pupil/iris and black sclera). These findings raise the possibility that the attentional effect implicated in the perception of a direct gaze is induced regardless of the stimulus context.     

Effects of study time and meaningfulness on environmental context-dependent recognition

In two experiments, we examined whether the size of place-context-dependent recognition decreased with study time and with the meaningfulness of the to-be-remembered materials. A group of 80 undergraduates intentionally studied a list of words in a short (1.5?s per item) or a long (4.0?s per item) study-time condition (Exp. 1). Another 40 undergraduates studied lists consisting of words and nonwords in the long-study-time condition (Exp. 2). After a short retention interval, recognition for the targets was tested in the same or in a different context. Context was manipulated by means of the combination of place, subsidiary task, and experimenter. Significant context-dependent recognition discrimination was found for words in the short-study-time condition (Exp. 1), but not in the long-study-time condition (Exps. 1 and 2). Significant effects were found as well for nonwords, even in the long-study-time condition (Exp. 2). These results are explained well by an outshining account: that is, by principles of outshining and encoding specificity.     

Context-dependent effects of background colour in free recall with spatially grouped words

Three experiments investigated context-dependent effects of background colour in free recall with groups of items. Undergraduates (N=113) intentionally studied 24 words presented in blocks of 6 on a computer screen with two different background colours. The two background colours were changed screen-by-screen randomly (random condition) or alternately (alternation condition) during the study period. A 30-second filled retention interval was imposed before an oral free-recall test. A signal for free recall was presented throughout the test on one of the colour background screens presented at study. Recalled words were classified as same- or different-context words according to whether the background colours at study and test were the same or different. The random condition produced significant context-dependent effects, whereas the alternation condition showed no context-dependent effects, regardless of whether the words were presented once or twice. Furthermore, the words presented on the same screen were clustered in recall, whereas the words presented against the same background colour but on different screens were not clustered. The present results imply: (1) background colours can cue spatially massed words; (2) background colours act as temporally local context; and (3) predictability of the next background colour modulates the context-dependent effect.     

The Ebbinghaus illusion deceives adults but not young children

The sensitivity of size perception to context has been used to distinguish between ‘vision for action’ and ‘vision for perception’, and to study cultural, psychopathological, and developmental differences in perception. The status of that evidence is much debated, however. Here we use a rigorous double dissociation paradigm based on the Ebbinghaus illusion, and find that for children below 7 years of age size discrimination is much less affected by surround size. Young children are less accurate than adults when context is helpful, but more accurate when context is misleading. Even by the age of 10 years context‐sensitivity is still not at adult levels. Therefore, size contrast as shown by the Ebbinghaus illusion is not a built‐in property of the ventral pathway subserving vision for perception but a late development of it, and low sensitivity to the Ebbinghaus illusion in autism is not primary to the pathology. Our findings also show that, although adults in Western cultures have low context‐sensitivity relative to East Asians, they have high context‐sensitivity relative to children. Overall, these findings reveal a gradual developmental trend toward ever broader contextual syntheses. Such developments are advantageous, but the price paid for them is that, when context is misleading, adults literally see the world less accurately than they did as children.     

Effects of illusory stripes on the Helmholtz illusion

This study examined the Helmholtz illusion by using "illusory stripes." A square patch is perceived as wider when vertical lines are drawn on it and is perceived as taller when horizontal lines are drawn on it, i.e., Helmholtz illusion. With vertical lines curved sinusoidally, horizontal "illusory stripes" are perceived; and with horizontal lines curved sinusoidally, vertical "illusory stripes" are perceived. The purpose of the present study was to test whether the "illusory stripes" produce the Helmholtz illusion. We measured the apparent size of a square patch filled with sinusoidal lines. Our subjects (N=27) judged the patch with horizontal "illusory stripes" taller than the square patch filled with vertical straight lines. The subjects also judged the square patch with vertical "illusory stripes" wider than the square patch filled with horizontal straight lines. These results demonstrate that "illusory stripes" can produce the Helmholtz illusion.