Visual extinction of similar and dissimilar stimuli: Evidence for level-dependent attentional competition

Repetition blindness (RB) is the failure to report a visual stimulus presented shortly after a first occurrence of the same stimulus (Kanwisher, 1987). A similar phenomenon is that visual extinction, the failure to identify a contralesional stimulus presented simultaneously with an ipsilesional stimulus, increases with increasing similarity between the contralesional and ipsilesional stimulus (Baylis, Driver, & Rafal, 1993). We report a patient who, after a right parietal stroke, presented increased extinction for letters in repeated (e.g., A + A) than in unrepeated (e.g., T + U) displays. Increased extinction due to RB was observed in all experimental conditions probing item identification and varied between 5.4% and 40.6% across conditions. RB was unaffected by temporal modulation of the display, but was significantly reduced when stimuli grouped by a surrounding contour. Identification of contralesional repeated and unrepeated letters could be enhanced by auditory cues presented prior to the visual display. These results suggest that perceptual processing of extinguished stimuli that are similar to the stimulus presented on the preserved side is relatively unimpaired, but that the patient fails to ascribe to the stimulus a separate identity, supporting the distinction between type recognition and token individuation (Kanwisher, 1987). The extinction patterns for similar and dissimilar stimuli indicate that competition for attentional selection does not only occur at low (perceptual) levels, but also at higher processing levels, suggesting the presence of attentional competition on different levels of analysis.     

Cerebral patterns of attentional habituation to emotional visual stimuli

Attentional habituation in response to emotional stimuli, an aspect of the interaction between cognitive and emotional processes that has received scant attention, was investigated. Event-related potentials were recorded using a 60-electrode array from 25 participants who attended to 120 presentations of three different picture types: emotionally negative (S-), positive (S+), and neutral (SO). The affective content of the stimulation was assessed, through questionnaires, by the participants themselves. N1 showed different patterns of habituation as a function of the stimulation: amplitudes indicated that S- was more resistant to habituation than SO and S+. This pattern, which reflects a greater capacity of S- to attract and maintain the participant's attention, is interpreted as a manifestation of the "negativity bias," a phenomenon that reflects an evolution-favored set of mechanisms that facilitate a rapid and intense response to aversive events.     

Reward and aversive stimuli produce similar nonphotic phase shifts

Circadian rhythms in rodents respond to arousing, nonphotic stimuli that contribute to daily patterns of entrainment. To examine whether the motivational significance of a stimulus is important for eliciting nonphotic circadian phase shirts in Syrian hamsters (Mesocricetus auratus), the authors compared responses to a highly rewarding stimulus (lateral hypothalamic brain stimulation reward [BSR]) and a highly aversive stimulus (footshock). Animals were housed on a 14:10-hr light-dark cycle until test day, when they were given a 1-hr BSR session (trained animals) or a 1-mA electric footshock at 1 of 8 circadian times, and were maintained in constant dark thereafter. Both BSR pulses and footshock produced nonphotic phase response curves. These results support the hypothesis that arousal resulting from the motivational significance of a stimulus is a major factor in nonphotic phase shifts.     

Evidence for an attentional component in saccadic inhibition of return

After presentation of a peripheral cue, facilitation at the cued location is followed by inhibition of return (IOR). It has been recently proposed that IOR may originate at different processing stages for manual and ocular responses, with manual IOR resulting from inhibited attentional orienting, and ocular IOR resulting form inhibited motor preparation. Contrary to this interpretation, we found an effect of target contrast on saccadic IOR. The effect of contrast decreased with increasing reaction times (RTs) for saccades, but not for manual key-press responses. This may have masked the effect of contrast on IOR with saccades in previous studies (Hunt and Kingstone in J Exp Psychol Hum Percept Perform 29:1068–1074, 2003) because only mean RTs were considered. We also found that background luminance strongly influenced the effects of gap and target contrast on IOR.

Grouping and Extinction: Evidence for Low-level Modulation of Visual Selection

The effects of collinear edge- and brightness-based grouping on extinction were investigated in a bilateral parietally damaged patient. If either edge or brightness information supported the grouping of two simultaneously presented items, extinction was reduced. Grouping reduced extinction when the items fell across the midline (Experiment 2) and when they were presented in either visual field (Experiment 3). However, even with edge- and brightness-based grouping cues present, a small increase in item-separation dramatically increased the extent of extinction, though single item detection remained constant. These results support a model of visual processing in which locally acting grouping processes (e.g. edge- and brightness-based grouping) provide input for a selection mechanism that processes the resulting structural units (cf. Duncan & Humphreys, 1989). Extinction reflects spatially biased competition for selection, which is reduced when elements form a single structural unit.     

Repeated downsizing contact: the effects of similar and dissimilar layoff experiences on work and well-being outcomes

In this longitudinal study, the authors compared 1,244 white- and blue-collar workers who reported 0, 1, or 2 contacts with layoffs; all were employees of a large manufacturing company that had engaged in several mass waves of downsizing. Consistent with a stress-vulnerability model, workers with a greater number of exposures to both direct and indirect downsizing reported significantly lower levels of job security and higher levels of role ambiguity, intent to quit, depression, and health problems. Findings did not support the idea that workers became more resilient as they encountered more layoff events. The authors found only partial evidence that the similarity or dissimilarity of the type of repeated downsizing exposure played a role in how workers reported changes in these outcome variables.     

Early somatosensory event-related potentials reveal attentional bias for internal stimuli in social anxiety

The present study used event-related brain potentials (ERPs) to investigate allocation of attentional resources to internal and external stimuli in individuals with social anxiety. High and low socially anxious individuals were presented with depictions of various facial expressions or household objects, followed by an internal (vibration presented to the finger) or external probe (the letter "E"). Participants were told that the vibration signals physiological changes and were asked to detect both probes. High socially anxious individuals showed larger front-central N140 amplitudes in response to vibratory internal probes as compared to non-anxious controls. ERPs elicited by picture stimuli and external probes and reaction times in response to both probe types did not differ between high and low social anxiety individuals. Early somatosensory ERPs reveal an attentional bias for internal stimuli that does not appear in overt behavior.     

Visual crowding and category specific deficits for pictorial stimuli: A neural network model

This paper describes a series of modular neural network simulations of visual object processing. In a departure from much previous work in this domain, the model described here comprises both supervised and unsupervised modules and processes real pictorial representations of items from different object categories. The unsupervised module carries out bottom-up encoding of visual stimuli, thereby developing a "perceptual" representation of each presented picture. The supervised component then classifies each perceptual representation according to a target semantic category. Model performance was assessed (1) during learning, (2) under generalisation to novel instances, and (3) after lesion damage at different stages of processing. Strong category effects were observed throughout the different experiments, with living things and musical instruments eliciting greater recognition failures relative to other categories. This pattern derives from within-category similarity effects at the level of perceptual representation and our data support the view that visual crowding can be a potentially important factor in the emergence of some category-specific impairments. The data also accord with the cascade model of object recognition, since increased competition between perceptual representations resulted in category-specific impairments even when the locus of damage was within the semantic component of the model. Some strengths and limitations of this modelling approach are discussed and the results are evaluated against some other accounts of category-specific recognition failure.     

Postural control during upper body locomotor-like movements: similar synergies based on dissimilar muscle modes

We studied the organization of leg and trunk muscles into groups (M-modes) and co-variation of M-mode involvement (M-mode synergies) during whole-body tasks associated with large variations of the moment of force about the vertical body axis. Our major questions were: (1) can muscle activation patterns during such tasks be described with a few M-modes common across tasks and subjects? (2) do these modes form the basis for synergies stabilizing M _z time pattern? (3) will this organization differ between an explicit body-rotation task and a task associated with locomotor-like alternating arm movements? Healthy subjects stood barefoot on the force platform and performed two motor tasks while paced by the metronome at 0.7, 1.0, and 1.4 Hz: cyclic rotation of the upper body about the vertical body axis (body-rotation task), and alternating rhythmic arm movements imitating those during running or quick walking (arm-movement task). Principal component analysis was used to identify three M-modes within the space of integrated indices of muscle activity. The M-mode vectors showed clustering neither across subjects nor across frequencies. Variance in the M-mode space across sway cycles was partitioned into two components, one that did not affect the average value of M _z shift (“good variance”) and the other that did. An index was computed reflecting the relative amount of the “good variance”; positive values of this index have been interpreted as reflecting a multi-M-mode synergy stabilizing the M _z trajectory. On average, the index was positive for both tasks and across all frequencies studied. However, the magnitude of the index was smaller for the intermediate frequency (1 Hz). The results show that the organization of muscles into groups during relatively complex whole-body tasks can differ significantly across both task variations and subjects. Nevertheless, the central nervous system seems to be able to build M _z stabilizing synergies based on different sets of M-modes, within the approach accepted in this study. The drop in the synergy index at the frequency of 1 Hz, which was close to the preferred movement frequency, may be interpreted as corroborating the neural origin of the M-mode co-variation.     

Colour-specific differences in attentional deployment for equiluminant pop-out colours: Evidence from lateralised potentials

We investigated how target colour affected behavioural and electrophysiological results in a visual search task. Perceptual and attentional mechanisms were tracked using the N2pc component of the event-related potential and other lateralised components. Four colours (red, green, blue, or yellow) were calibrated for each participant for luminance through heterochromatic flicker photometry and equated to the luminance of grey distracters. Each visual display contained 10 circles, 1 colored and 9 grey, each of which contained an oriented line segment. The task required deploying attention to the colored circle, which was either in the left or right visual hemifield. Three lateralised ERP components relative to the side of the lateral coloured circle were examined: a posterior contralateral positivity (Ppc) prior to N2pc, the N2pc, reflecting the deployment of visual spatial attention, and a temporal and contralateral positivity (Ptc) following N2pc. Red or blue stimuli, as compared to green or yellow, had an earlier N2pc. Both the Ppc and Ptc had higher amplitudes to red stimuli, suggesting particular selectivity for red. The results suggest that attention may be deployed to red and blue more quickly than to other colours and suggests special caution when designing ERP experiments involving stimuli in different colours, even when all colours are equiluminant.     

Hyperplasia of similar and dissimilar mucosa adjoining gastric mucosal wounds in the rat.

Deep mucosal wounds were produced within 1 mm of the squamo-columnar junction of the stomach of the rat, either on the squamous or on the glandular side, and the response of both the regenerating epithelium and of the adjoining, dissimilar epithelium was studied 24 hours to 12 weeks later. Squamous epithelium, both overlying previously injured squamous areas and adjoining previously injured glandular areas showed distinct hyperplasia that began on the 3rd day and was still present at 12 weeks. Glandular epithelium overlying previously injured glandular areas and adjoining previously injured squamous areas showed no hyperplasia but modulation of parietal and chief cells into mucus-secreting cells with increased mitosis. These changes appear more likely the effects of non-specific mitogenic agents than of reduced concentration of epithelial chalones.     

An attentional inhibitory deficit for irrelevant information in obsessive-compulsive disorder: Evidence from ERPs

Previous studies on attentional bias have demonstrated that patients with obsessive–compulsive disorder (OCD) have an overall longer reaction time (RT) for various stimuli. It was hypothesized that this general slowness may indicate the presence of an attentional inhibition deficit in OCD. To test the hypothesis, event-related potentials (ERPs) were recorded in 31 non-medicated OCD patients and 29 age-, handedness- and sex-matched healthy controls while they performed an emotional Stroop task (EST). Relative to the control subjects, the OCD patients had similar interference effects for negative words, but an overall longer RT and larger P2 and P3 amplitudes to all words. These results support the notion that OCD is characterized by an attentional inhibitory dysfunction for irrelevant information.     

Hand deviations toward distractors Evidence for response competition

It has been suggested that, when movements are planned within cluttered environments, competing responses programmed to distracting stimuli are inhibited based on their relation to the action being performed. Further, as a result of this inhibition, the path of the movement made to the target object deviates away from the distractor. In contrast to the object avoidance hypothesis, the results of the present study show that, for aiming movements made in environments in which distractors are present, the path of the movement veers toward the distractor. Moreover, the effects of the distractors on the movement trajectory were independent of the direction of limb movement. These findings suggest that, when a distractor is not a potential physical barrier, a response to the distractor may be activated along with the target response and, owing to temporal advantages, cause a deviation of the movement trajectory toward the distractor.     

Pupil dilation indicates the coding of past prediction errors: Evidence for attentional learning theory

The attentional learning theory of Pearce and Hall ( 1980 ) predicts more attention to uncertain cues that have caused a high prediction error in the past. We examined how the cue‐elicited pupil dilation during associative learning was linked to such error‐driven attentional processes. In three experiments, participants were trained to acquire associations between different cues and their appetitive (Experiment 1), motor (Experiment 2), or aversive (Experiment 3) outcomes. All experiments were designed to examine differences in the processing of continuously reinforced cues (consistently followed by the outcome) versus partially reinforced, uncertain cues (randomly followed by the outcome). We measured the pupil dilation elicited by the cues in anticipation of the outcome and analyzed how this conditioned pupil response changed over the course of learning. In all experiments, changes in pupil size complied with the same basic pattern: During early learning, consistently reinforced cues elicited greater pupil dilation than uncertain, randomly reinforced cues, but this effect gradually reversed to yield a greater pupil dilation for uncertain cues toward the end of learning. The pattern of data accords with the changes in prediction error and error‐driven attention formalized by the Pearce‐Hall theory.     

Evidence for an attentional component of inhibition of return in visual search

Inhibition of return (IOR) is typically described as an inhibitory bias against returning attention to a recently attended location as a means of promoting efficient visual search. Most studies examining IOR, however, either do not use visual search paradigms or do not effectively isolate attentional processes, making it difficult to conclusively link IOR to a bias in attention. Here, we recorded ERPs during a simple visual search task designed to isolate the attentional component of IOR to examine whether an inhibitory bias of attention is observed and, if so, how it influences visual search behavior. Across successive visual search displays, we found evidence of both a broad, hemisphere‐wide inhibitory bias of attention along with a focal, target location‐specific facilitation. When the target appeared in the same visual hemifield in successive searches, responses were slower and the N2pc component was reduced, reflecting a bias of attention away from the previously attended side of space. When the target occurred at the same location in successive searches, responses were facilitated and the P1 component was enhanced, likely reflecting spatial priming of the target. These two effects are combined in the response times, leading to a reduction in the IOR effect for repeated target locations. Using ERPs, however, these two opposing effects can be isolated in time, demonstrating that the inhibitory biasing of attention still occurs even when response‐time slowing is ameliorated by spatial priming.     

Perceptual reversals of Necker stimuli during intermittent presentation with limited attentional resources

During prolonged viewing of ambiguous stimuli, such as Necker cubes, sudden perceptual reversals occur from one perceptual interpretation to another. The role of attention in such reversals is not clear. We tested whether perceptual reversals depend on attentional resources by manipulating perceptual load and recording event‐related potentials (ERPs) during intermittent presentation of Necker stimuli. The results did not reveal any influence for perceptual load on the frequency of reversals. The ERPs showed that perceptual load influenced electrophysiological activity over parieto‐central areas in the P1 time window (110–140 ms), but load did not modify the early enhancements of positivity (30–140 ms), which correlated with perceptual reversals at occipito‐temporal sites. We conclude that disambiguation of ambiguous figures is based on early mechanisms that can work efficiently with only a minimal amount of attentional resources.