Direction Specific Biases in Human Visual and Vestibular Heading Perception

Heading direction is determined from visual and vestibular cues. Both sensory modalities have been shown to have better direction discrimination for headings near straight ahead. Previous studies of visual heading estimation have not used the full range of stimuli, and vestibular heading estimation has not previously been reported. The current experiments measure human heading estimation in the horizontal plane to vestibular, visual, and spoken stimuli. The vestibular and visual tasks involved 16 cm of platform or visual motion. The spoken stimulus was a voice command speaking a heading angle. All conditions demonstrated direction dependent biases in perceived headings such that biases increased with headings further from the fore-aft axis. The bias was larger with the visual stimulus when compared with the vestibular stimulus in all 10 subjects. For the visual and vestibular tasks precision was best for headings near fore-aft. The spoken headings had the least bias, and the variation in precision was less dependent on direction. In a separate experiment when headings were limited to ±45°, the biases were much less, demonstrating the range of headings influences perception. There was a strong and highly significant correlation between the bias curves for visual and spoken stimuli in every subject. The correlation between visual-vestibular and vestibular-spoken biases were weaker but remained significant. The observed biases in both visual and vestibular heading perception qualitatively resembled predictions of a recent population vector decoder model (Gu et al., 2010) based on the known distribution of neuronal sensitivities.     

Visual Perception: Larger Is Faster

A recent study has shown that neurons in the inferior temporal cortex of the macaque monkey brain show earlier selectivity to global and large shapes than to local and small ones, which may underlie the faster behavioral responses to global aspects of a scene.     

Relationships between Categorical Perception of Phonemes,Phoneme Awareness,and Visual Attention Span in Developmental Dyslexia

We tested the hypothesis that the categorical perception deficit of speech sounds in developmental dyslexia is related to phoneme awareness skills, whereas a visual attention (VA) span deficit constitutes an independent deficit. Phoneme awareness tasks, VA span tasks and categorical perception tasks of phoneme identification and discrimination using a d/t voicing continuum were administered to 63 dyslexic children and 63 control children matched on chronological age. Results showed significant differences in categorical perception between the dyslexic and control children. Significant correlations were found between categorical perception skills, phoneme awareness and reading. Although VA span correlated with reading, no significant correlations were found between either categorical perception or phoneme awareness and VA span. Mediation analyses performed on the whole dyslexic sample suggested that the effect of categorical perception on reading might be mediated by phoneme awareness. This relationship was independent of the participants’ VA span abilities. Two groups of dyslexic children with a single phoneme awareness or a single VA span deficit were then identified. The phonologically impaired group showed lower categorical perception skills than the control group but categorical perception was similar in the VA span impaired dyslexic and control children. The overall findings suggest that the link between categorical perception, phoneme awareness and reading is independent from VA span skills. These findings provide new insights on the heterogeneity of developmental dyslexia. They suggest that phonological processes and VA span independently affect reading acquisition.     

A Study in Classification: Style and Visual Perception

The authors explore the process by which people determine that one object is similar to, or different from, another, and investigate how the process might affect our understanding of archaeological classification. Exploratory Data Analysis [Tukey] was conducted on measurements from 159 conical fired pots excavated at al-Hiba in Iraq. Although frequency distributions of single parameters did not show clear and consistent categories, certain correlated parameters showed a clear bimodal frequency distribution into two basic shapes which matched the traditional archaeological subdivision into “cups” and “bowls.” Stylistic subdivisions perceived by undergraduate students (91, from Brooklyn College and New York University), when asked to sort profile drawings of pots (73) into perceived divisions and then group divisions into styles, agreed with the bimodal objective division. Exploratory Data Analysis can identify objective stylistic grouping of archaeological artifacts.

Other findings of the authors during the conduct of this research include: (1) shape, independent of size, divides these pots into cups or bowls; (2) uniformity of surface and core colors indicates no basic differences in clays, kilns, or firing temperature and durations for nearly 1,000 years; (3) there is little inter-observer consistency in the division of the two major categories of perceived styles, but gender clearly affects the number of observed subdivisions. The study concludes with a look at statistical analyses of style in other objects and works of art and briefly explores some of the benefits that might accrue from the continued study of visual perception and art.     

The Attention Modulation on Timing: An Event-Related Potential Study

The present study examined the neural mechanisms of attention modulation on timing using ERP and sLORETA measurements in a dual-task paradigm. We parametrically varied the attention to the durations of a 1000-Hz pure tone and further localized the cortical regions that were sensitive to the attention modulation on timing. Results demonstrated that the attention modulation might happen at early stage, approximately 200 ms after stimulus presentation. The P2 component at frontal area served as an early neural correlate of attention effects on timing. More importantly, the contingent negative variation (CNV) appeared at fronto-central area was sensitive to the attention effect. In addition, the supplementary motor area (SMA) was assumed to be one of the key regions for selectively attending to and estimating time. These findings provide temporal and spatial correlates of attention-modulated time processing and potentially help to investigate the neural mechanisms of patients with time perception deficits.     

Pre-Saccadic Shifts of Visual Attention

The locations of visual objects to which we attend are initially mapped in a retinotopic frame of reference. Because each saccade results in a shift of images on the retina, however, the retinotopic mapping of spatial attention must be updated around the time of each eye movement. Mathôt and Theeuwes [1] recently demonstrated that a visual cue draws attention not only to the cue''s current retinotopic location, but also to a location shifted in the direction of the saccade, the “future-field”. Here we asked whether retinotopic and future-field locations have special status, or whether cue-related attention benefits exist between these locations. We measured responses to targets that appeared either at the retinotopic or future-field location of a brief, non-predictive visual cue, or at various intermediate locations between them. Attentional cues facilitated performance at both the retinotopic and future-field locations for cued relative to uncued targets, as expected. Critically, this cueing effect also occurred at intermediate locations. Our results, and those reported previously [1], imply a systematic bias of attention in the direction of the saccade, independent of any predictive remapping of attention that compensates for retinal displacements of objects across saccades [2].     

Race Guides Attention in Visual Search

It is known that faces are rapidly and even unconsciously categorized into social groups (black vs. white, male vs. female). Here, I test whether preferences for specific social groups guide attention, using a visual search paradigm. In Experiment 1 participants searched displays of neutral faces for an angry or frightened target face. Black target faces were detected more efficiently than white targets, indicating that black faces attracted more attention. Experiment 2 showed that attention differences between black and white faces were correlated with individual differences in automatic race preference. In Experiment 3, using happy target faces, the attentional preference for black over white faces was eliminated. Taken together, these results suggest that automatic preferences for social groups guide attention to individuals from negatively valenced groups, when people are searching for a negative emotion such as anger or fear.     

Neural Effects of Auditory Distraction on Visual Attention in Schizophrenia

Sensory flooding, particularly during auditory stimulation, is a common problem for patients with schizophrenia. The functional consequences of this impairment during cross-modal attention tasks, however, are unclear. The purpose of this study was to examine how auditory distraction differentially affects task-associated response during visual attention in patients and healthy controls. To that end, 21 outpatients with schizophrenia and 23 healthy comparison subjects performed a visual attention task in the presence or absence of distracting, environmentally relevant “urban” noise while undergoing functional magnetic resonance imaging at 3T. The task had two conditions (difficult and easy); task-related neural activity was defined as difficult – easy. During task performance, a significant distraction (noise or silence) by group (patient or control) interaction was observed in the left dorsolateral prefrontal cortex, right hippocampus, left temporoparietal junction, and right fusiform gyrus, with patients showing relative hypoactivation during noise compared to controls. In patients, the ability to recruit the dorsolateral prefrontal cortex during the task in noise was negatively correlated with the effect of noise on reaction time. Clinically, the ability to recruit the fusiform gyrus during the task in noise was negatively correlated with SANS affective flattening score, and hippocampal recruitment during the task in noise was positively correlated with global functioning. In conclusion, schizophrenia may be associated with abnormalities in neural response during visual attention tasks in the presence of cross-modal noise distraction. These response differences may predict global functioning in the illness, and may serve as a biomarker for therapeutic development.     

The Commingled Division of Visual Attention

Many critical activities require visual attention to be distributed simultaneously among distinct tasks where the attended foci are not spatially separated. In our two experiments, participants performed a large number of trials where both a primary task (enumeration of spots) and a secondary task (reporting the presence/absence or identity of a distinctive shape) required the division of visual attention. The spots and the shape were commingled spatially and the shape appeared unpredictably on a relatively small fraction of the trials. The secondary task stimulus (the shape) was reported in inverse proportion to the attentional load imposed by the primary task (enumeration of spots). When the shape did appear, performance on the primary task (enumeration) suffered relative to when the shape was absent; both speed and accuracy were compromised. When the secondary task required identification in addition to detection, reaction times increased by about 200 percent. These results are broadly compatible with biased competition models of perceptual processing. An important area of application, where the commingled division of visual attention is required, is the augmented reality head-up display (AR-HUD). This innovation has the potential to make operating vehicles safer but our data suggest that there are significant concerns regarding driver distraction.