Chia-huei Tseng

Subjective discriminability of invisibility: a framework for distinguishing perceptual and attentional failures of awareness

Conscious visual perception can fail in many circumstances. However, little is known about the causes and processes leading to failures of visual awareness. In this study, we introduce a new signal detection measure termed subjective discriminability of invisibility (SDI) that allows one to distinguish between subjective blindness due to reduction of sensory signals or to lack of attentional access to sensory signals. The SDI is computed based upon subjective confidence in reporting the absence of a target (i.e., miss and correct rejection trials). Using this new measure, we found that target misses were subjectively indistinguishable from physical absence when contrast reduction, backward masking and flash suppression were used, whereas confidence was appropriately modulated when dual task, attentional blink and spatial uncertainty methods were employed. These results show that failure of visual perception can be identified as either a result of perceptual or attentional blindness depending on the circumstances under which visual awareness was impaired.

Long-lasting sensitization to a given colour after visual search

Visual attention enables an observer to select specific visual information for processing. In an ambiguous motion task in which a coloured grating can be perceived as moving in either of two opposite directions depending on the relative salience of two colours in the display, attending to one of the colours influences the direction in which the grating appears to move. Here, we use this secondary effect of attention in a motion task to measure the effect of attending to a specific colour in a search task. Observers performed a search task in which they searched for a target letter in a 4 × 4 coloured matrix. Each of the 16 squares within a matrix was assigned one of four colours, and observers knew that the target letter would appear on only one of these colours throughout the experiment. Observers performed the ambiguous motion task before and after the search task. Attending to a particular colour for a brief period in the search task profoundly influenced the perceived direction of motion. This effect lasted for up to one month and in some cases had to be reversed by practising searches for the complementary colour, indicating a much longer-persisting effect of attention than has been observed previously.

Beyond the classical receptive field: The effect of contextual stimuli

Following the pioneering studies of the receptive field (RF), the RF concept gained further significance for visual perception by the discovery of input effects from beyond the classical RF. These studies demonstrated that neuronal responses could be modulated by stimuli outside their RFs, consistent with the perception of induced brightness, color, orientation, and motion. Lesion scotomata are similarly modulated perceptually from the surround by RFs that have migrated from the interior to the outer edge of the scotoma and in this way provide filling-in of the void. Large RFs are advantageous to this task. In higher visual areas, such as the middle temporal and inferotemporal lobe, RFs increase in size and lose most of their retinotopic organization while encoding increasingly complex features. Whereas lower-level RFs mediate perceptual filling-in, contour integration, and figure-ground segregation, RFs at higher levels serve the perception of grouping by common fate, biological motion, and other biologically relevant stimuli, such as faces. Studies in alert monkeys while freely viewing natural scenes showed that classical and nonclassical RFs cooperate in forming representations of the visual world. Today, our understanding of the mechanisms underlying the RF is undergoing a quantum leap. What had started out as a hierarchical feed-forward concept for simple stimuli, such as spots, lines, and bars, now refers to mechanisms involving ascending, descending, and lateral signal flow. By extension of the bottom-up paradigm, RFs are nowadays understood as adaptive processors, enabling the predictive coding of complex scenes. Top-down effects guiding attention and tuned to task-relevant information complement the bottom-up analysis.

Collinearity Impairs Local Element Visual Search

In visual searches, stimuli following the law of good continuity attract attention to the global structure and receive attentional priority. Also, targets that have unique features are of high feature contrast and capture attention in visual search. We report on a salient global structure combined with a high orientation contrast to the background, which actually impairs the search for a local element. In a search display containing 21 × 27 short horizontal element bars, we rotated the orientation of a whole column by 90° so that it stood out as a salient vertical collinear column. Observers searched for a small tilt on one of the elemental bars, and the target only occasionally overlapped with the salient column (overlapping targets) by chance. In other words, the collinear column was not informative about a target search and was task-irrelevant. Our results showed that the target tilt orientation was discerned more slowly and less accurately for overlapping targets than nonoverlapping targets. In five experiments, we demonstrated that collinear grouping on the salient distractor was the major cause of this impairment. Potential mechanisms of how a global structure interacts with perceptual salience are discussed.

Rapid-eye-movement-sleep (REM) associated enhancement of working memory performance after a daytime nap

The main objective was to study the impact of a daytime sleep opportunity on working memory and the mechanism behind such impact. This study adopted an experimental design in a sleep research laboratory. Eighty healthy college students (Age:17-23, 36 males) were randomized to either have a polysomnography-monitored daytime sleep opportunity (Nap-group, n=40) or stay awake (Wake-group, n=40) between the two assessment sessions. All participants completed a sleep diary and wore an actigraph-watch for 5 days before and one day after the assessment sessions. They completed the state-measurement of sleepiness and affect, in addition to a psychomotor vigilance test and a working memory task before and after the nap/wake sessions. The two groups did not differ in their sleep characteristics prior to and after the lab visit. The Nap-group had higher accuracy on the working memory task, fewer lapses on the psychomotor vigilance test and lower state-sleepiness than the Wake-group. Within the Nap-group, working memory accuracy was positively correlated with duration of rapid eye movement sleep (REM) and total sleep time during the nap. Our findings suggested that “sleep gain” during a daytime sleep opportunity had significant positive impact on working memory performance, without affecting subsequent nighttime sleep in young adult, and such impact was associated with the duration of REM. While REM abnormality has long been noted in pathological conditions (e.g. depression), which are also presented with cognitive dysfunctions (e.g. working memory deficits), this was the first evidence showing working memory enhancement associated with REM in daytime napping in college students, who likely had habitual short sleep duration but were otherwise generally healthy.

The Relation Among Sleep Duration, Homework Burden, and Sleep Hygiene in Chinese School-Aged Children

Insufficient sleep in school-aged children is common in modern society, with homework burden being a potential risk factor. The aim of this article is to explore the effect of sleep hygiene on the association between homework and sleep duration. Children filled out the Chinese version of the Adolescent Sleep Hygiene Scale, and parents filled out a sociodemographic questionnaire. The final sample included 363 boys and 371 girls with a mean age of 10.82 ± 0.38 years. Children with more homework went to bed later and slept less. Better sleep hygiene was associated with earlier bedtimes and longer sleep duration. Findings suggest that homework burden had a larger effect on sleep duration than sleep hygiene. Fifth-grade children in Shanghai have an excessive homework burden, which overwrites the benefit of sleep hygiene on sleep duration.

When motion appears stopped: stereo motion standstill.

Motion standstill is different from the usual perceptual experiences associated with objects in motion. In motion standstill, a pattern that is moving quite rapidly is perceived as being motionless, and yet its details are not blurred but clearly visible. We revisited motion standstill in dynamic random-dot stereograms similar to those first used by Julesz and Payne [Julesz B, Payne R (1968) Vision Res 8:433–444]. Three improvements were made to their paradigm to avoid possible confounds: The temporal frequency of the motion stimuli was manipulated independently from that of individual stereo gratings so that the failure of motion perception is not due to inability to compute stereo. The motion of the stereo gratings was continuous across the visual field so that the perceived pattern in motion standstill was not a simple average of a back-and-forth display wobble over time. Observers discriminated three spatial frequencies to demonstrate pattern recognition. Three objective psychophysical methods, instead of merely self-report, were used to objectively demonstrate motion standstill. Our results confirm that motion standstill occurs in dynamic random-dot stereogram motion displays at 4–6 Hz. Motion standstill occurs when the stimulus spatiotemporal frequency combination exceeds that of the salience-based third-order motion system in a spatiotemporal frequency range in which the shape and depth systems still function. The ability of shape systems to extract a representative image from a series of moving samples is a significant component of a biological systems ability to derive a stable perceptual world from a constantly changing visual environment.

Constructing a metrics for blur perception with blur discrimination experiments

In this study, we measured blur discrimination threshold at different blur levels. We found that the discrimination threshold first decreased and then increased again as reference edge width blur increased. This dipper shape of the blur discrimination threshold vs. reference width functions (TvW) functions can be explained by a divisive inhibition model. The first stage of the model contains a linear operator whose excitation is the inner product of the image and the sensitivity profile of the operator. The response of the blur discrimination mechanism is the power function of the excitation of the linear operator divided by the sum of the divisive inhibition and an additive factor. Changing mean luminance of the edge has little effect on blur discrimination except at very low luminance. When luminance is low, the blur discrimination was higher at small reference blur than those measured at medium to high luminance. This difference diminished at large reference blur. Such luminance effect can be explained by a change in the additive factor in the model. Reducing contrast of the edge shifted the whole TvW function up vertically. This effect can be explained by the decrease of gain factors in the linear operator. With these results, we constructed a metric for blur perception from the divisive inhibition we proposed and tested in this study.

Orientation is different: Interaction between contour integration and feature contrasts in visual search

Salient items usually capture attention and are beneficial to visual search. Jingling and Tseng (2013), nevertheless, have discovered that a salient collinear column can impair local visual search. The display used in that study had 21 rows and 27 columns of bars, all uniformly horizontal (or vertical) except for one column of bars orthogonally oriented to all other bars, making this unique column of collinear (or noncollinear) bars salient in the display. Observers discriminated an oblique target bar superimposed on one of the bars either in the salient column or in the background. Interestingly, responses were slower for a target in a salient collinear column than in the background. This opens a theoretical question of how contour integration interacts with salience computation, which is addressed here by an examination of how salience modulated the search impairment from the collinear column. We show that the collinear column needs to have a high orientation contrast with its neighbors to exert search interference. A collinear column of high contrast in color or luminance did not produce the same impairment. Our results show that orientation-defined salience interacted with collinear contour differently from other feature dimensions, which is consistent with the neuronal properties in V1.

Salient collinear grouping diminishes local salience in visual search: An eye movement study

Our eyes and attention are easily attracted to salient items in search displays. When a target is spatially overlapped with a salient distractor (overlapping target), it is usually detected more easily than when it is not (nonoverlapping target). Jingling and Tseng (2013), however, found that a salient distractor impaired visual search when the distractor was comprised of more than nine bars collinearly aligned to each other. In this study, we examined whether this search impairment is due to reduction of salience on overlapping targets. We used the short-latency saccades as an index for perceptual salience. Results showed that a long collinear distractor decreases perceptual salience of local overlapping targets in comparison to nonoverlapping targets, reflected by a smaller proportion of the short-latency saccades. Meanwhile, a salient noncollinear distractor increases salience of overlapping targets. Our results led us to conclude that a long collinear distractor diminishes the perceptual salience of the target, a factor which poses a counter-intuitive condition in which a target on a salient region becomes less salient. We discuss the possible causes for our findings, including crowding, the global precedence effect, and the filling-in of a collinear contour.