Examining Increment thresholds as a function of pedestal contrast under hypothetical parvo- and magnocellular-biased conditions.

Theoretically, the pulsed- and steady-pedestal paradigms are thought to track contrast-increment thresholds (ΔC) as a function of pedestal contrast (C) for the parvocellular (P) and magnocellular (M) systems, respectively, yielding linear ΔC versus C functions for the pulsed- and nonlinear functions for the steady-pedestal paradigm. A recent study utilizing these paradigms to isolate the P and M systems reported no evidence of the M system being suppressed by red light, contrary to previous physiological and psychophysical findings. Curious as to why this may have occurred, we examined how ΔC varies with C for the P and M systems using the pulsed- and steady-pedestal paradigms and stimuli biased towards the P or M systems based on their sensitivity to spatial frequency (SF) and color. We found no effect of color and little influence of SF. To explain this lack of color effects, we used a quantitative model of ΔC (as it changes with C) to obtain Csat and contrast-gain values. The contrast-gain values (i) contradicted the hypothesis that the steady-pedestal paradigm tracks the M-system response, and (ii) our obtained Csat values indicated strongly that both pulsed- and steady-pedestal paradigms track primarily the P-system response.

Visual Memory Scan Slopes: Their Changes over the First Two Seconds of Processing.

Using the prime-probe comparison paradigm, Jacob, Breitmeyer, and Treviño (2013) demonstrated that information processing in visual short-term memory (VSTM) proceeds through three stages: sensory visible persistence (SVP), nonvisible informational persistence (NIP), and visual working memory (VWM). To investigate the effect of increasing the memory load on these stages by using 1, 3, and 5 display items, measures of VSTM performance, including storage, storage-slopes, and scan-slopes, were obtained. Results again revealed three stages of VSTM processing, but with the NIP stage increasing in duration as memory load increased, suggesting a need, during the NIP stage, for transfer and encoding delays of information into VWM. Consistent with this, VSTM scan-slopes, in ms/item, were lowest during the first NIP stage, highest during the second NIP stage, and intermediate during the third, non-sensory VWM stage. The results also demonstrated a color-superiority effect, as all VSTM scan-slopes for color were lower than those for shape and as all VSTM storages for color are greater than those for shape, and the existence of systematic pair-wise correlations between all three measures of VSTM performance. These findings and their implications are related to other paradigms and methods used to investigate post-stimulus processing in VSTM.

Interactions between visual working memory and visual attention among survivors of pediatric acute lymphoblastic leukemia (ALL) and their healthy peers.

Introduction: There is increasing concern for adverse cognitive late effects among survivors of pediatric acute lymphoblastic leukemia (ALL) given the widespread impact they have on academic achievement, particularly working memory and attention. We assessed performance among survivors and their healthy peers on a dual task paradigm measuring visual working memory (VWM) and visual attention independently and the dynamic relationship between the two. Assessing specific subsets within cognitive domains allows for understanding the distinct nature of cognitive impairments. Method: Participants were 34 survivors of ALL who have been off-treatment and disease free for 7.5 years; and 20 healthy controls, all between the ages of 10 and 18 years. We utilized behavioral single- and dual-task paradigms. In the dual tasks, participants maintained several items in VWM while performing a visual attention task (Eriksen Flanker Task) that required processing of a target stimulus while inhibiting the processing of distractor stimuli. The single tasks involved performing only the VWM task or only the visual attention task. Results: Results revealed survivors of ALL performed significantly worse than their healthy peers on the single visual attention task but not the single VWM task. Of particular interest, group differences were obtained on the dual VWM and visual attention tasks, such that the VWM and attention tasks reciprocally interfered with each other only among survivors and not their healthy peers. Conclusions: Our results highlight a core deficit in visual attention that is exacerbated by VWM demands among survivors of ALL. The implementation of tasks from cognitive neuroscience paradigms may be sensitive to cognitive impairments experienced by cancer survivors. Assessment and intervention practices among survivors of pediatric ALL are discussed.

Contrast sensitivity indicates processing level of visual illusions.

A nearly linear contrast response function (CRF) is found in the lower level striate cortex whereas a steep, nonlinear increase at lower contrasts that gradually increases toward response saturation for higher contrasts is found in the higher level extrastriate cortex. This change of CRFs along the ventral cortical pathway indicates a shift from stimulus- and energy-dependent coding at lower levels to percept- and information-dependent coding at higher levels. The increase of nonlinearity at higher levels optimizes the extraction of perceptual information by amplifying responses to the ubiquitous low-contrast inputs in the environment. We used this difference of CRFs between lower and higher levels, particularly at lower contrasts (.0 to .30), as a tool to investigate examples of 2 lower level (simultaneous brightness and simultaneous tilt) and 2 higher level (Poggendorff and Ponzo) illusions. As predicted, the Poggendorff and Ponzo illusions yielded strong nonlinear increases in their CRFs compared to the more linear functions found for the simultaneous-brightness and simultaneous-tilt illusions. We conclude that the Poggendorff-Ponzo illusions rely more heavily on high-level, percept-dependent cortical processing than do the simultaneous-brightness-simultaneous-tilt illusions and, more generally, that differences between contrast-dependent changes may be a useful tool in determining the relative level of cortical processing of many other visual effects. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Can Contrast-Response Functions Indicate Visual Processing Levels?

Many visual effects are believed to be processed at several functional and anatomical levels of cortical processing. Determining if and how the levels contribute differentially to these effects is a leading problem in visual perception and visual neuroscience. We review and analyze a combination of extant psychophysical findings in the context of neurophysiological and brain-imaging results. Specifically using findings relating to visual illusions, crowding, and masking as exemplary cases, we develop a theoretical rationale for showing how relative levels of cortical processing contributing to these effects can already be deduced from the psychophysically determined functions relating respectively the illusory, crowding and masking strengths to the contrast of the illusion inducers, of the flankers producing the crowding, and of the mask. The wider implications of this rationale show how it can help to settle or clarify theoretical and interpretive inconsistencies and how it can further psychophysical, brain-recording and brain-imaging research geared to explore the relative functional and cortical levels at which conscious and unconscious processing of visual information occur. Our approach also allows us to make some specific predictions for future studies, whose results will provide empirical tests of its validity.

Psychophysical "blinding" methods reveal a functional hierarchy of unconscious visual processing.

Numerous non-invasive experimental "blinding" methods exist for suppressing the phenomenal awareness of visual stimuli. Not all of these suppressive methods occur at, and thus index, the same level of unconscious visual processing. This suggests that a functional hierarchy of unconscious visual processing can in principle be established. The empirical results of extant studies that have used a number of different methods and additional reasonable theoretical considerations suggest the following tentative hierarchy. At the highest levels in this hierarchy is unconscious processing indexed by object-substitution masking. The functional levels indexed by crowding, the attentional blink (and other attentional blinding methods), backward pattern masking, metacontrast masking, continuous flash suppression, sandwich masking, and single-flash interocular suppression, fall at progressively lower levels, while unconscious processing at the lowest levels is indexed by eye-based binocular-rivalry suppression. Although unconscious processing levels indexed by additional blinding methods is yet to be determined, a tentative placement at lower levels in the hierarchy is also given for unconscious processing indexed by Troxler fading and adaptation-induced blindness, and at higher levels in the hierarchy indexed by attentional blinding effects in addition to the level indexed by the attentional blink. The full mapping of levels in the functional hierarchy onto cortical activation sites and levels is yet to be determined. The existence of such a hierarchy bears importantly on the search for, and the distinctions between, neural correlates of conscious and unconscious vision.

Exploring facial emotion perception in schizophrenia using transcranial magnetic stimulation and spatial filtering.

Schizophrenia patients have difficulty extracting emotional information from facial expressions. Perception of facial emotion can be examined by systematically altering the spatial frequency of stimuli and suppressing visual processing with temporal precision using transcranial magnetic stimulation (TMS). In the present study, we compared 25 schizophrenia patients and 27 healthy controls using a facial emotion identification task. Spatial processing was examined by presenting facial photographs that contained either high (HSF), low (LSF), or broadband/unfiltered (BSF) spatial frequencies. Temporal processing was manipulated using a single-pulse TMS delivered to the visual cortex either before (forward masking) or after (backward masking) photograph presentation. Consistent with previous studies, schizophrenia patients performed significantly below controls across all three spatial frequencies. A spatial frequency by forward/backward masking interaction effect demonstrated reduced performance in the forward masking component in the BSF condition and a reversed performance pattern in the HSF condition, with no significant differences between forward and backward masking in the LSF condition. However, the group by spatial frequency interaction was not significant. These findings indicate that manipulating visual suppression of emotional information at the level of the primary visual cortex results in comparable effects on both groups. This suggests that patients' deficits in facial emotion identification are not explained by low-level processes in the retino-geniculo-striate projection, but may rather depend on deficits of affect perception occurring at later integrative processing stages.

Contributions of magno- and parvocellular channels to conscious and non-conscious vision.

The dorsal and ventral cortical pathways, driven predominantly by magnocellular (M) and parvocellular (P) inputs, respectively, assume leading roles in models of visual information processing. Although in prior proposals, the dorsal and ventral pathways support non-conscious and conscious vision, respectively, recent modelling and empirical developments indicate that each pathway plays important roles in both non-conscious and conscious vision. In these models, the ventral P-pathway consists of one subpathway processing an object's contour features, e.g. curvature, the other processing its surface attributes, e.g. colour. Masked priming studies have shown that feed-forward activity in the ventral P-pathway on its own supports non-conscious processing of contour and surface features. The dorsal M-pathway activity contributes directly to conscious vision of motion and indirectly to object vision by projecting to prefrontal cortex, which in turn injects top-down neural activity into the ventral P-pathway and there 'ignites' feed-forward-re-entrant loops deemed necessary for conscious vision. Moreover, an object's shape or contour remains invisible without the prior conscious registration of its surface properties, which for that reason are taken to comprise fundamental visual qualia. Besides suggesting avenues for future research, these developments bear on several recent and past philosophical issues.

Tracking the first two seconds: three stages of visual information processing?

We compared visual priming and comparison tasks to assess information processing of a stimulus during the first 2 s after its onset. In both tasks, a 13-ms prime was followed at varying SOAs by a 40-ms probe. In the priming task, observers identified the probe as rapidly and accurately as possible; in the comparison task, observers determined as rapidly and accurately as possible whether or not the probe and prime were identical. Priming effects attained a maximum at an SOA of 133 ms and then declined monotonically to zero by 700 ms, indicating reliance on relatively brief visuosensory (iconic) memory. In contrast, the comparison effects yielded a multiphasic function, showing a maximum at 0 ms followed by a minimum at 133 ms, followed in turn by a maximum at 240 ms and another minimum at 720 ms, and finally a third maximum at 1,200 ms before declining thereafter. The results indicate three stages of prime processing that we take to correspond to iconic visible persistence, iconic informational persistence, and visual working memory, with the first two used in the priming task and all three in the comparison task. These stages are related to stages presumed to underlie stimulus processing in other tasks, such as those giving rise to the attentional blink.

Assessing temporal processing of facial emotion perception with transcranial magnetic stimulation.

The ability to process facial expressions can be modified by altering the spatial frequency of the stimuli, an effect that has been attributed to differential properties of visual pathways that convey different types of information to distinct brain regions at different speeds. While this effect suggests a potential influence of spatial frequency on the processing speed of facial emotion, this hypothesis has not been examined directly. We addressed this question using a facial emotion identification task with photographs containing either high spatial frequency (HSF), low spatial frequency (LSF), or broadband spatial frequency (BSF). Temporal processing of emotion perception was manipulated by suppressing visual perception with a single-pulse transcranial magnetic stimulation (TMS), delivered to the visual cortex at six intervals prior to (forward masking) or following (backward masking) stimulus presentation. Participants performed best in the BSF, followed by LSF, and finally HSF condition. A spatial frequency by forward/backward masking interaction effect demonstrated reduced performance in the forward masking component in the BSF condition and a reversed performance pattern in the HSF condition, with no significant differences between forward and backward masking in the LSF condition. Results indicate that LSF information may play a greater role than HSF information in emotional processing, but may not be sufficient for fast conscious perception of emotion. As both LSF and HSF filtering reduced the speed of extracting emotional information from faces, it is possible that intact BSF faces have an inherent perceptual advantage and hence benefit from faster temporal processing.

Object substitution masking in schizophrenia: an event-related potential analysis.

Schizophrenia patients exhibit deficits on visual processing tasks, including visual backward masking, and these impairments are related to deficits in higher-level processes. In the current study we used electroencephalography techniques to examine successive stages and pathways of visual processing in a specialized masking paradigm, four-dot masking, which involves masking by object substitution. Seventy-six schizophrenia patients and 66 healthy controls had event-related potentials (ERPs) recorded during four-dot masking. Target visibility was manipulated by changing stimulus onset asynchrony (SOA) between the target and mask, such that performance decreased with increasing SOA. Three SOAs were used: 0, 50, and 100 ms. The P100 and N100 perceptual ERPs were examined. Additionally, the visual awareness negativity (VAN) to correct vs. incorrect responses, an index of reentrant processing, was examined for SOAs 50 and 100 ms. Results showed that patients performed worse than controls on the behavioral task across all SOAs. The ERP results revealed that patients had significantly smaller P100 and N100 amplitudes, though there was no effect of SOA on either component in either group. In healthy controls, but not patients, N100 amplitude correlated significantly with behavioral performance at SOAs where masking occurred, such that higher accuracy correlated with a larger N100. Healthy controls, but not patients, exhibited a larger VAN to correct vs. incorrect responses. The results indicate that the N100 appears to be related to attentional effort in the task in controls, but not patients. Considering that the VAN is thought to reflect reentrant processing, one interpretation of the findings is that patients' lack of VAN response and poorer performance may be related to dysfunctional reentrant processing.

Spatial attention effects during conscious and nonconscious processing of visual features and objects.

Flanker congruency effects were measured in a masked flanker task to assess the properties of spatial attention during conscious and nonconscious processing of form, color, and conjunctions of these features. We found that (1) consciously and nonconsciously processed colored shape distractors (i.e., flankers) produce flanker congruency effects; (2) these congruency effects decrease with increasing separation between the probe and the flanking stimuli; (3) this decrease occurs even when flankers are suppressed from awareness; and (4) regardless of whether the form, color, or conjunction of these features have to be attended. Importantly, (5) flanker congruency effects decrease at nearly comparable rates when flankers are visible or masked, which suggests that for separate and conjoint features (i.e., objects), the gradient of spatial attention at the conscious and nonconscious levels of processing is almost identical, with the possibility of a slightly broader gradient for nonconsciously processed visual information.

Nonconscious and conscious color priming in schizophrenia.

Deficits in visual processing are well established in schizophrenia. However, there is conflicting evidence about whether these deficits start before the formation of percepts because visual processing studies in schizophrenia have typically examined the processing of consciously registered stimuli. In this study, we used nonconscious color priming to evaluate the very early visual processing stages in schizophrenia. Nonconscious and conscious color priming was assessed in 148 schizophrenia patients and 54 healthy control subjects. In both conditions, subjects identified the color of a ring preceded by a disk (prime) in the same color (congruent) or a different color (incongruent). The ring rendered the disk invisible in the nonconscious condition (SOA of 62.5 ms) or did not mask the disk (SOA of 200 ms) in the conscious condition. Schizophrenia patients exhibited a color priming effect (longer reaction times in the incongruent vs. congruent trials) that was similar to healthy controls in both the nonconscious and conscious priming conditions. Healthy controls had a significantly larger priming effect in the nonconscious vs. conscious condition, but patients did not show a significant difference in priming effects between the two conditions. Our results indicate that schizophrenia patients do not have deficits at the nonconscious, pre-perceptual stages of visual processing, suggesting that the feed forward sweep of information processing (from retina to V1) might be intact in schizophrenia. These results imply that the well-documented visual processing deficits in this illness likely occur at later, percept-dependent stages of processing.

Microgenesis of surface completion in visual objects: evidence for filling-out.

Using metacontrast masking we examined the temporal dynamics of surface completion in object vision. By varying the stimulus onset asynchrony between the target object and the flanking mask(s), we obtained estimates of the time required for the entire surface contrast to fill out within the area delimited by the contours/edges of the target. The estimated speed of the filling-out process was 36.0 deg/s. Using existing estimates of cortical magnification, the computed filling-out speed in terms of cortical distance is .385 m/s, a value that approximates the estimated cortical filling-in speed and the speed of horizontal propagation in monkey V1. We discuss our results in relation to (1) prior findings of filling-in and filling-out phenomena, using surface completion in cortical space as the unifying principle, and (2) extant computational models of object vision.

Metacontrast masking with texture-defined second-order stimuli.

We examine metacontrast masking with texture-defined second-order stimuli. Our results reveal that (1) the monotonic type A as well as the nonmonotonic (U-shaped) type B metacontrast effect, which has been extensively examined with first-order luminance-defined stimuli, can be obtained with texture-defined second-order stimuli; and (2) while variations of luminance contrast are known to affect the magnitude of metacontrast with first-order stimuli, neither the size nor orientation contrast between texture elements defining the second-order stimuli have a significant impact on the magnitude or shape of metacontrast. These findings bear on theories of metacontrast masking by showing that the mechanism giving rise to nonmonotonic masking effects can operate beyond the level of first-order stimulus processing.

Visual consciousness revisited: magnocellular and parvocellular contributions to conscious and nonconscious vision.

Current theoretical approaches to consciousness and vision associate the dorsal cortical pathway, in which magnocellular (M) input is dominant, with nonconscious visual processing and the ventral cortical pathway, in which parvocellular (P) input is dominant, with conscious visual processing. We explored the known differences between M and P contrast-response functions to investigate the roles of these channels in vision. Simulations of contrast-dependent priming revealed that priming effects obtained with unmasked, visible primes were best modeled by equations characteristic of M channel responses, whereas priming effects obtained with masked, invisible primes were best modeled by equations characteristic of P channel responses. In the context of current theoretical approaches to conscious and nonconscious processing, our results indicate a surprisingly significant role of M channels in conscious vision. In a broader discussion of the role of M channels in vision, we propose a neurophysiologically plausible interpretation of the present results: M channels indirectly contribute to conscious object vision via top-down modulation of reentrant activity in the ventral object-recognition stream.