Visual demand and visual field presentation influence natural scene processing.

BACKGROUND: Bottom-up and top-down processes are involved in visual analysis of scenes. Here we examined the influence of top-down visual demand on natural scene processing. METHODS: We measured accuracy and response time in adults performing two stimuli-equivalent tasks. Unfiltered, low or high spatial frequency (SF) natural scenes were presented in central, left, or right visual fields (CVF, LVF, RVF). The tasks differed only by the instructed visual demand. In the detection task, participants had to decide whether a scene was present or not. In the categorization task, they had to decide whether the scene was a city or a forest. RESULTS: Higher accuracy was seen for the LVF in the detection task, but for categorization, greater accuracy was seen for the RVF. The interaction between Task and SF revealed coarse-to-fine processing in the categorization task for both accuracy and reaction time, which nearly disappeared in the detection task. Considering the interaction of Task, VF and SF, a left-hemisphere specialisation (i.e., RVF advantage) was observed for the categorisation of HSF scenes for accuracy alone, whereas a LVF advantage was seen for all SFs in the detection task for both accuracy and reaction time. CONCLUSION: Our results revealed that the nature of top-down visual demand is essential to understanding how visual analysis is achieved in each hemisphere. Moreover, this study examining the effects of visual demand, visual field presentation, and SF content of stimuli through the use of ecological stimuli provides a tool to enrich the clinical examination of visual and neurovisual patients.

Bisections in two languages: when number processing, spatial representation, and habitual reading direction interact.

Calabria and Rossetti (2005) demonstrated that spatial biases related to the mental number line can be seen even when bisecting strings of number words. Strings of smaller magnitude number words were bisected further to the left than strings of larger magnitude number words. The current study investigated whether the left-to-right mental number line associated with number processing will result in similar spatial biases despite a habitual, right-to-left reading direction. Monolingual left-to-right readers were compared to bidirectional readers of English and Hebrew. Strings of Arabic numerals and of number words (e.g., THREE, EIGHT) were presented in separate conditions of English and Hebrew. Significant rightward biases were seen among native Hebrew readers, regardless of English reading level; whereas native English readers (both bidirectional and monodirectional) did not show significant biases to either the left or the right. The spatial bias in bisecting either Arabic numeral strings or number words was related to the habitual reading direction of the participant. There was no difference in spatial bias or for frequency of spatial bias based on numerical magnitude for either condition. We discuss the influence of cultural factors, such as reading direction and proficiency, on the representation of spatial and numerical material.

Assessment of visuo-attentional abilities in young children with or without visual disorder: toward a systematic screening in the general population.

In young children, visual attention, analysis or memory is only rarely evaluated. Moreover, tools to test for such higher-order visual capacities in children are limited. In an attempt to develop and refine such tools, we selected nine tests to assess visuo-attentional abilities before formal reading education (grade 1). The battery consisted of gaze fixation, visual field, visual extinction, binocular visual pursuit, visual memory, "A" cancellation, Teddy bears cancellation, embedded figures, and matching tasks. This battery was used in the general population (n=110) to calculate cut-off scores identifying the lower 5% of the general population to obtain a screening measure for neurovisual disabilities in children. To evaluate our battery's sensitivity and specificity to neurovisual disorders over ophthalmological diseases, a neurovisual group (n=9) and an ophthalmologic group (n=13) also completed the tests. Overall, all but three tests of the battery could be used to discriminate between neurovisual and ophthalmologic children. The ophthalmologic children failed the visual field extent examination and the cancellation tasks, consistent with deleterious effects of ophthalmologic disease on visual perception as well as higher-order vision. Using the cut-off scores, the battery identified only 2 out of 13 ophthalmologic patients, but 5 out of 9 neurovisual patients. In the general population, these cut-off scores identified seven children. These children were previously undiagnosed with any disability (i.e., no diagnosis of ophthalmological, neurological, or psychiatric disease) and thus did not receive any rehabilitation. This preliminary study highlights the necessity for a neurovisual disorder screening tool for young children.

Egocentric reference in bidirectional readers as measured by the straight-ahead pointing task.

The present study aimed to show that bidirectional reading and language exposure influence the position of egocentric reference (ER), the perceived direction of the body's sagittal axis proposed to act as an anchor for movements in extracorporeal space. Directional factors (e.g., visual scanning bias and reading habits) have been proposed to influence visuospatial performance, such as in line bisection and figure drawing. In past studies, bidirectional readers have been less consistent in demonstrating a bias compared to unidirectional readers. Using a straight-ahead pointing task to assess egocentric reference, we compared 14 unidirectional left-to-right readers (Uni-LR) to three bidirectional reading groups that differed in the reading direction of their native language and/or the level of their second language literacy: 16 low-English literate, native right-to-left, bidirectional readers (Lo-Bi-RL), 13 high-English literate, native right-to-left, bidirectional readers (Hi-Bi-RL), and 15 native left-to-right, bidirectional readers (Bi-LR). Participants were asked to point straight-ahead while blindfolded using either a left-to-right or a right-to-left scanning direction to approach the subjective sagittal midline. Uni-LRs showed left-side spatial bias when scanning left-to-right and right-side bias during right-to-left scanning, Bi-LRs and Lo-Bi-RLs (i.e., intermediate level or less in their second language) demonstrated the opposite pattern, and Hi-Bi-RLs showed left-side spatial bias regardless of scanning direction. Results are discussed in terms of accuracy and spatial bias regarding the interaction between reading direction and spatial cognition based on the level of bidirectional literacy and language exposure.

Facial expression during emotional monologues in unilateral stroke: an analysis of monologue segments.

Emotional monologues of brain-damaged subjects were examined to determine whether interhemispheric or intrahemispheric differences exist for facial emotional expression. A special feature was the comparison of expressions produced during the initial, middle, and last segments of the monologues. Videotaped emotional and non-emotional monologues from the New York Emotion Battery (Borod, Welkowitz, & Obler, 1992) of eight right brain-damaged (RBD), eight left brain-damaged (LBD), and eight normal control (NC) subjects, with matching for demographics and lesion location, were rated. Five raters were trained to evaluate the emotional intensity and category accuracy of the facial expressions produced during these monologues. Results revealed some support for a reversed valence effect, with RBDs showing relatively less accurate performance during positive monologues. Intrahemispheric results revealed that, overall, RBDs with frontal lobe lesions showed the least intense facial expressions. Segment analysis found that individuals produced facial expressions with significantly more emotional intensity during the middle and last thirds of the monologues than during the initial third of the monologues. Findings indicate intrahemispheric as well as interhemispheric differences in facial emotional expression and suggest the utilization of the latter parts of monologues in the evaluation of emotional expression, which has potential clinical implications.