Interaction between top-down decision-driven congruency effect and bottom-up input-driven congruency effect is correlated with conscious awareness.

In a conventional (Stroop) priming paradigm, it was well documented that objective prime-target incongruency delays response time (RT) to target compared to prime-target congruent condition. Recent evidence suggests that incongruency between the target and subjectively reported prime identity also delays RT over and above the classic congruency effect. When the prime is rendered invisible, the former effect is fundamentally a bottom-up (BU) stimulus-driven congruency effect and the latter a top-down (TD) guess-driven congruency effect. An influential theory of consciousness, global neuronal workspace theory, postulates that the long-lasting simultaneous and reciprocal interaction between TD decision network and BU input network is preserved during conscious processing and disabled during unconscious processing. Current study is focused on testing this theoretical postulation using two behavioral experiments. Our results showed that indeed TD-congruency and BU-congruency produced additive RT effects on prime-invisible trials, which implies that TD and BU prime representations are activated in independent neuronal populations. Meanwhile, an underadditive interaction effect was observed as prime visibility rose, which is a signature that TD and BU prime representations recruited overlapping neuronal populations during conscious perception. In addition, we suggest that current behavioral paradigm might be a financially friendly alternative to detect the presence of representational overlap in the brain between a wide range of mental representations, such as expectation, prediction, conscious/unconscious perception, and conscious/unconscious working memory. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Spatial suppression of chromatic motion.

Center-surround antagonism, as a ubiquitous feature in visual processing, usually leads to inferior perception for a large stimulus compared to a small one. For example, it is more difficult to judge the motion direction of a large high-contrast pattern than that of a small one. However, this spatial suppression in the motion dimension was only reported for luminance motion, and was not found for chromatic motion. Given that center-surround suppression only occurs for strong visual inputs, we hypothesized that previous failure in finding spatial suppression of chromatic motion might be due to weak chromatic motion being induced with stimuli of limited parameters. In this study, we used phase-shift discrimination and motion-direction discrimination tasks to measure motion spatial suppression induced by stimuli of two spatial frequencies (0.5 and 2 cpd) and two contrasts (low and high). We found that spatial suppression of the chromatic motion was stably observed for stimuli of high spatial frequency (2 cpd) and high contrast and spatial summation occurred for stimuli of low spatial frequency (0.5 cpd). Intriguingly, there was no correlations between the motion spatial suppressions of luminance motion and chromatic motion, implying that the two types of spatial suppression are not originated from the same neural processing. Our findings indicate that spatial suppression also exists for chromatic motion, and the mechanisms underlying the spatial suppression of chromatic motion is different from that of luminance motion.

Attentional effect on contrast appearance: From enhancement to attenuation.

Does attention alter appearance? Recent studies have shown that an exogenous cue tends to increase the perceived contrast of a low-contrast stimulus. In the present study we systematically studied the attentional effect over a wide range of contrast levels (15% to 60%). Besides replicating the enhancement at lower contrast levels with higher comparative tasks (Experiment 1), the data revealed a cue-induced attenuation in apparent contrast at higher contrast levels with lower comparative tasks (Experiment 2) and same/different judgment task (Experiment 3). This attenuation effect was robust at the individual level, and it was not due to response bias or sensory interactions (Experiments 3 and 4). These results suggest that attention modulates contrast appearance and this effect depends on both the contrast level and the type of judgment task used. We propose that our findings can be understood through contrast gain mechanism on supersatuating neurons, whose response increases first as the stimulus intensity increases, but decrease the responses after the peak. This surprising phenomenon offers insights for the underlying neural mechanisms of visual processing. (PsycINFO Database Record

Hemispheric asymmetry in the influence of language on visual perception.

Many studies have shown that language can affect visual perception; however, our understanding of the neural basis of linguistic influence is inadequate. This can be investigated by examining the hemispheric asymmetry of linguistic influence. The left and right hemispheres are dominant in close and distant semantic processing, respectively. In this study, we investigated whether the hemispheric asymmetry of semantic processing led to hemispheric asymmetry for concept priming on the detection of objects degraded by continuous flash suppression. We combined a priming paradigm with the divided visual field paradigm and used continuous flash suppression, which renders objects invisible. The results indicated that the hemispheric asymmetry of semantic processing led to a right lateralization in the influence of more abstract concepts on visual perception. The lateralization of brain connectomes may be the underlying neural basis of this effect.

Temporal expectancy modulates phasic alerting in both detection and discrimination tasks.

The aim of the present study was to investigate whether phasic alerting might be modulated by temporal expectancy and to determine the processing stages at which this modulation might occur. We manipulated participants' expectancy for the target appearance by systematically varying the cue-target stimulus onset asynchrony (SOA) distribution in both detection and discrimination tasks. There were three temporal expectancy conditions: the non-aging condition in which temporal expectancy was eliminated, the aging condition in which temporal expectancy increased as SOA increased, and the accelerated-aging condition in which temporal expectancy increased more dramatically as SOA increased than in the aging condition. We obtained the same pattern of results in both detection and discrimination tasks: the onset time of the alerting effect was postponed successively across the three temporal expectancy conditions. The present findings suggest that the time course of the alerting effect may be modulated by temporal expectancy, highlighting the importance of taking account into the influence of temporal expectancy in studies involving the time course of cognitive processes. Furthermore, since mechanisms underlying the detection and discrimination tasks may differ in early processing stages involving perceptual analysis and response selection, the same result pattern observed in both tasks is consistent with the hypothesis that the modulation of temporal expectancy on phasic alerting occurs at late processing stages involving motor preparation.

Interactions between surround suppression and interocular suppression in human vision.

Several types of suppression phenomena have been observed in the visual system. For example, the ability to detect a target stimulus is often impaired when the target is embedded in a high-contrast surround. This contextual modulation, known as surround suppression, was formerly thought to occur only in the periphery. Another type of suppression phenomena is interocular suppression, in which the sensitivity to a monocular target is reduced by a superimposed mask in the opposite eye. Here, we explored how the two types of suppression operating across different spatial regions interact with one another when they simultaneously exert suppressive influences on a common target presented at the fovea. In our experiments, a circular target grating presented to the fovea of one eye was suppressed interocularly by a noise pattern of the same size in the other eye. The foveal stimuli were either shown alone or surrounded by a monocular annular grating. The orientation and eye-of-origin of the surround grating were varied. We found that the detection of the foveal target subjected to interocular suppression was severely impaired by the addition of the surround grating, indicating strong surround suppression in the fovea. In contrast, when the interocular suppression was released by superimposing a binocular fusion ring onto both the target and the dichoptic mask, the surround suppression effect was found to be dramatically decreased. In addition, the surround suppression was found to depend on the contrast of the dichoptic noise with the greatest surround suppression effect being obtained only when the noise contrast was at an intermediate level. These findings indicate that surround suppression and interocular suppression are not independent of each other, but there are strong interactions between them. Moreover, our results suggest that strong surround suppression may also occur at the fovea and not just the periphery.

Alerting and orienting of attention without visual awareness.

Two types of the attentional network, alerting and orienting, help organisms respond to environmental events for survival in the temporal and spatial dimensions, respectively. Here, we applied chromatic flicker beyond the critical fusion frequency to address whether awareness was necessary for activation of the two attentional networks. We found that high-frequency chromatic flicker, despite its failure to reach awareness, produced the alerting and orienting effects, supporting the dissociation between attention and awareness. Furthermore, as the flicker frequency increased, the orienting effect attenuated whereas the alerting effect remained unchanged. According to the systematic decline in temporal frequency sensitivity across the visual hierarchy, this finding suggests that unconscious alerting might be associated with activity in earlier visual areas than unconscious orienting. Since high-frequency flicker has been demonstrated to only activate early visual cortex, we suppose that neural activation in early visual areas might be sufficient to activate the two attentional networks.

Attentional capture is contingent on the interaction between task demand and stimulus salience.

The aim of this research was to investigate the potential impacts of task demand and stimulus salience on the stimulus-driven attentional capture effect. The participants performed an inefficient visual search task while an irrelevant luminance singleton was present. In Experiment 1, the task demand was manipulated while the stimulus salience of the irrelevant singleton was fixed. With the same salient singleton, the attentional capture effect was observed in the low-difficulty condition but disappeared in the high-difficulty condition. In Experiment 2, the stimulus salience was manipulated while the task demand was fixed. With the same task, the highly salient singleton captured attention, whereas the relatively lowly salient singleton could not. In Experiment 3, both task demand and stimulus salience were manipulated simultaneously. The stimulus-driven attentional capture effect by the irrelevant singleton increased not only as the task demand decreased but also as the stimulus salience increased. The present study might provide a way to reconcile conflicting findings in the attentional capture literature; the underlying neural mechanism is discussed.

Stimulus-driven attentional capture by equiluminant color change.

The aim of this research was to investigate the mechanisms underlying stimulus-driven attentional capture by feature changes in basic dimensions, and we chose color for the present investigation. In Experiment 1, participants searched for a target letter among colored disks containing distractor letters while a disk underwent color change. Although color change was irrelevant to the task and uninformative about the target position, we found a strong form of stimulus-driven attentional capture. Experiment 2 demonstrated that salient color discontinuity per se could not capture attention, ruling out the possibility that the capture effect we observed might be due to color discontinuity. In Experiment 3, we observed the capture effect by color change again in a more optimized experimental design. The present findings show that color change captures attention, supporting our view that dynamic feature changes can capture attention in a stimulus-driven manner.