Joseph A. Harris

Sandwich masking eliminates both visual awareness of faces and face-specific brain activity through a feedforward mechanism

It is generally agreed that considerable amounts of low-level sensory processing of visual stimuli can occur without conscious awareness. On the other hand, the degree of higher level visual processing that occurs in the absence of awareness is as yet unclear. Here, event-related potential (ERP) measures of brain activity were recorded during a sandwich-masking paradigm, a commonly used approach for attenuating conscious awareness of visual stimulus content. In particular, the present study used a combination of ERP activation contrasts to track both early sensory-processing ERP components and face-specific N170 ERP activations, in trials with versus without awareness. The electrophysiological measures revealed that the sandwich masking abolished the early face-specific N170 neural response (peaking at ~170 ms post-stimulus), an effect that paralleled the abolition of awareness of face versus non-face image content. Furthermore, however, the masking appeared to render a strong attenuation of earlier feedforward visual sensory-processing signals. This early attenuation presumably resulted in insufficient information being fed into the higher level visual system pathways specific to object category processing, thus leading to unawareness of the visual object content. These results support a coupling of visual awareness and neural indices of face processing, while also demonstrating an early low-level mechanism of interference in sandwich masking.

Neural processing stages during object-substitution masking and their relationship to perceptual awareness.

The extent of visual perceptual processing that occurs in the absence of awareness is as yet unclear. Here we examined event-related-potential (ERP) indices of visual and cognitive processes as awareness was manipulated through object-substitution masking (OSM), an awareness-disrupting effect that has been hypothesized to result from the disruption of reentrant signaling to low-level visual cortical areas. In OSM, a visual stimulus array is briefly presented that includes a parafoveal visual target denoted by a cue, typically consisting of several surrounding dots. When the offset of the target-surrounding cue dots is delayed relative to the rest of the array, a striking reduction in the perception of the target image surrounded by the dots is observed. Using faces and houses as the target stimuli, we found that successful OSM reduced or eliminated all the measured electrophysiological indices of visual processing stages after 130ms post-stimulus. More specifically, when targets were missed within the masked condition (i.e., on trials with effective OSM that disrupted awareness), we observed fully intact early feed-forward processing up through the visual extrastriate P1 ERP component peaking at 100ms, followed by reduced low-level activity over the occipital pole 130-170ms post-stimulus, reduced ERP indices of lateralized shifts of attention toward the parafoveal target, reduced object-generic visual processing, abolished object-category-specific (face-specific) processing, and reduced late visual short-term-memory processing activity. The results provide a comprehensive electrophysiological account of the neurocognitive underpinnings of effective OSM of visual-object images, including evidence for central roles of early reentrant signal disruption and insufficient visual attentional deployment.

Widespread temporo-occipital lobe dysfunction in amyotrophic lateral sclerosis

Recent studies suggest that amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) lie on a single clinical continuum. However, previous neuroimaging studies have found only limited involvement of temporal lobe regions in ALS. To better delineate possible temporal lobe involvement in ALS, the present study aimed to examine changes in functional connectivity across the whole brain, particularly with regard to extra-motor regions, in a group of 64 non-demented ALS patients and 38 healthy controls. To assess between-group differences in connectivity, we computed edge-level statistics across subject-specific graphs derived from resting-state functional MRI data. In addition to expected ALS-related decreases in functional connectivity in motor-related areas, we observed extensive changes in connectivity across the temporo-occipital cortex. Although ALS patients with comorbid FTD were deliberately excluded from this study, the pattern of connectivity alterations closely resembles patterns of cerebral degeneration typically seen in FTD. This evidence for subclinical temporal dysfunction supports the idea of a common pathology in ALS and FTD.

Disruption of Visual Awareness during the Attentional Blink Is Reflected by Selective Disruption of Late-stage Neural Processing

Any information represented in the brain holds the potential to influence behavior. It is therefore of broad interest to determine the extent and quality of neural processing of stimulus input that occurs with and without awareness. The attentional blink is a useful tool for dissociating neural and behavioral measures of perceptual visual processing across conditions of awareness. The extent of higher-order visual information beyond basic sensory signaling that is processed during the attentional blink remains controversial. To determine what neural processing at the level of visual-object categorization occurs in the absence of awareness, electrophysiological responses to images of faces and houses were recorded both within and outside the attentional blink period during a rapid serial visual presentation stream. Electrophysiological results were sorted according to behavioral performance (correctly identified targets vs. missed targets) within these blink and nonblink periods. An early index of face-specific processing (the N170, 140- to 220-msec poststimulus) was observed regardless of whether the participant demonstrated awareness of the stimulus, whereas a later face-specific effect with the same topographic distribution (500- to 700-msec poststimulus) was only seen for accurate behavioral discrimination of the stimulus content. The present findings suggest a multistage process of object-category processing, with only the later phase being associated with explicit visual awareness.

Reward-associated features capture attention in the absence of awareness: Evidence from object-substitution masking.

Reward-associated visual features have been shown to capture visual attention, evidenced in faster and more accurate behavioral performance, as well as in neural responses reflecting lateralized shifts of visual attention to those features. Specifically, the contralateral N2pc event-related-potential (ERP) component that reflects attentional shifting exhibits increased amplitude in response to task-relevant targets containing a reward-associated feature. In the present study, we examined the automaticity of such reward-association effects using object-substitution masking (OSM) in conjunction with MEG measures of visual attentional shifts. In OSM, a visual-search array is presented, with the target item to be detected indicated by a surrounding mask (here, four surrounding squares). Delaying the offset of the target-surrounding four-dot mask relative to the offset of the rest of the target/distracter array disrupts the viewers awareness of the target (masked condition), whereas simultaneous offsets do not (unmasked condition). Here we manipulated whether the color of the OSM target was or was not of a previously reward-associated color. By tracking reward-associated enhancements of behavior and the N2pc in response to masked targets containing a previously rewarded or unrewarded feature, the automaticity of attentional capture by reward could be probed. We found an enhanced N2pc response to targets containing a previously reward-associated color feature. Moreover, this enhancement of the N2pc by reward did not differ between masking conditions, nor did it differ as a function of the apparent visibility of the target within the masked condition. Overall, these results underscore the automaticity of attentional capture by reward-associated features, and demonstrate the ability of feature-based reward associations to shape attentional capture and allocation outside of perceptual awareness.

An electrophysiological marker of the desire to quit in smokers.

For many smokers, the motivational state of craving is a central feature of their dependence on nicotine, and is often at odds with a general desire to quit. How this desire to quit may influence the craving for a cigarette, however, is unclear. In the current study, we manipulated the level of craving in 24 regular smokers, and recorded EEG measures of brain activity during a rare target detection task utilizing addiction‐unrelated stimuli. In response to the non‐targets, we observed that smokers wanting to quit showed an enhanced late frontal activation when they were craving vs. not craving, whereas smokers not wanting to quit showed the opposite pattern of activity. A dissociation was also present in the target‐related P300 response as a function of craving and desire to quit, with smokers who did not want to quit processing targets differentially between the states of craving and non‐craving. The data suggest that distinct top‐down control mechanisms during craving may be implemented by people who wish to quit smoking, as compared to those who do not wish to quit. This pattern of findings establishes this ERP activity as a potential biomarker that may help to differentiate people who want to quit their addiction from those who wish to continue to use their substance of choice.

EEG measures of brain activity reveal that smoking-related images capture the attention of smokers outside of awareness

ABSTRACT The capture of attention by substance‐related stimuli in dependent users is a major factor in the maintenance and/or cessation of substance use. The present study examined the automaticity of this process in smokers, as well as the effects of craving. Event‐related potential (ERP) measures of spatial‐attention allocation (N2pc) and extended target processing (SPCN) were isolated during an object‐substitution masking (OSM) task that disrupted the perceptual visibility of smoking‐related and office‐related targets. Each participant completed two experimental sessions: one in which they were deprived of nicotine for a period of several hours prior to the session (craving), and one before which they were allowed to smoke (non‐craving). Results were consistent with an account of automatic attentional capture by smoking‐related images outside of awareness, with masked trials yielding a selective enhancement of the attention‐sensitive N2pc in response to these images, but in the absence of a corresponding behavioral enhancement on those trials. Finally, the manipulation of craving appeared to increase the overall task demand, yielding an enhancement of the SPCN component across target type and masking conditions. Together, these results suggest that smoking‐related visual stimuli in the environment can capture the attention of smokers outside of awareness, in what seems to be an automatic process. HIGHLIGHTSAttentional biases with respect to addiction‐related stimuli have been reported.The automaticity of these biases, and any interactions with craving, are unknown.EEG used to track attention to smoking‐related images during substitution masking.Attentional capture by smoking images seen only in masked conditions, craving or not.Suggests an automatic process that smokers can otherwise suppress.

Neural correlates of training-induced improvements of calculation skills in patients with brain lesions

PURPOSE The loss of calculation skills due to brain lesions leads to a major reduction in the quality of life and is often associated with difficulties of returning to work and a normal life. Very little is known about the neural mechanisms underlying performance improvement due to calculation training during rehabilitation. The current study investigates the neural basis of training-induced changes in patients with acalculia following ischemic stroke or traumatic brain lesions. METHODS Functional hemodynamic responses (fMRI) were recorded in seven patients during calculation and perceptual tasks both before and after acalculia training. RESULTS Despite the heterogeneity of brain lesions associated with acalculia in our patient sample, a common pattern of training-induced changes emerged. Performance improvements were associated with widespread deactivations in the prefrontal cortex. These deactivations were calculation-specific and only observed in patients exhibiting a considerable improvement after training. CONCLUSION These findings suggest that the training-induced changes in our patients rely on an increase of frontal processing efficiency.

Object-Category Processing, Perceptual Awareness, and the Role of Attention during Motion-Induced Blindness

Perceptual information represented in the brain, whether a viewer is aware of it or not, holds the potential to influence subsequent behavior. Here we tracked a well-established event-related-potential (ERP) measure of visual-object-category processing, the face-specific ventrolateral-occipital N170 response, across conditions of perceptual awareness. To manipulate perceptual awareness, we employed the motion-induced-blindness (MIB) paradigm, in which covertly attended, static, visual-target stimuli that are superimposed on a globally moving array of distractors perceptually disappear and reappear. Subjects responded with a button press when the target images (faces and houses) actually physically occurred (and thus perceptually appeared) and when they perceptually reappeared after an MIB episode. A comparison of the face-specific N170 ERP activity (face-vs-house responses) revealed robust face-selective ERP activity for physically appearing images and no such activity for perceptual reappearances following MIB episodes, suggesting that face-specific processing had continued uninterrupted during MIB. In addition, electrophysiological activity preceding an actual appearance of a target image, collapsed across face and house image types, was compared to that preceding the perceptual reappearance of a continuously present image (following MIB). This comparison revealed a parietally distributed positive-polarity response that preceded only reappearances following MIB. Such a result suggests a possible role of parietally mediated attentional capture by the present-but-suppressed target in the reestablishment of perceptual awareness at the end of an MIB episode. The present results provide insight into the level of visual processing that can occur in the absence of awareness, as well as into the mechanisms underlying MIB and its influence on perceptual awareness.

Identity Matters: Schooling the Student Body in Academic Discourse

What are writing teachers to do when faced with difference? Do we try to help students acquire the distinctive idioms of academic discourse, to write as we do? Or do we respect their home languages and resist asking them to assimilate? Donna LeCourt notes that, when she first began work on Identity Matters, she planned to argue for a familiar middle position in this debate, one that urges teachers to help students draw on the ‘multiple voices’ – of home, work, community, school – that they all already possess in learning how to write for the academy (190). Instead her book turned into an exploration of why such a hybrid style proves so hard to teach and learn. LeCourt grounds her study in a reading of 46 ‘literacy autobiographies’ – about half of which are written by undergraduate ‘basic writers’ and the other half written by graduate students in English at ‘a large midwestern university’ in the US (9). She reasons that both groups are faced with acquiring a new discourse – either of ‘academic writing’ or of ‘English studies’ – and thus that they have much to tell us about what it might mean to forge a new identity as a writer. That seems fair enough, although I wish that LeCourt had spent more time setting up the context of her study. We never find out, for instance, exactly what a ‘literacy autobiography’ is, or what sort of assignments students wrote them in response to, or how one is placed as a ‘basic writer’ at Midwestern U, or what kinds of careers the English grad students there imagine themselves as training for. Rather, we must glean what we can of these writers through her brief quotations of their prose. And that prose turns out to be suggestive and compelling. Both the basic writers and grad students write eloquently about their past experiences and current struggles with writing. Many express high levels of anxiety about the writing tasks they are now being asked to take on. Few seem to feel they can build on their past successes with writing to succeed in that work – a worry which seems to belie the notion that academic writing allows for a blending of diverse voices. LeCourt argues, to the contrary, that academic writing is neither multivocal nor ‘transparent’, but rather reflects the values of the dominant culture. She identifies two different problems faced by student writers who are not male or white or middle class but who must still try to master this discourse. On the one hand, there are writers, usually African Americans, who do indeed retain two voices, but who feel they must keep their ‘home’ and ‘academic’ identities separate. On the other hand, there are writers, often from the working class, who abandon their home discourses in order to assume the language of the academy. The choice is to compartmentalize or to pass. Either results in anxiety. Changing English Vol. 18, No. 3, September 2011, 331–333