Visual masking during the attentional blink: tests of the object substitution hypothesis

When 2 masked targets are presented in a rapid sequence, correct identification of the 1st hinders identification of the 2nd. Visual masking of the 2nd target plays a critical role during this 2nd-target deficit, or "attentional blink" (AB). The object substitution hypothesis (B. Giesbrecht & V. Di Lollo, 1998) predicts that late-stage visual processes involved in object substitution mediate masking of the 2nd target during AB, whereby stronger masking should produce a more severe deficit. Six experiments are presented, together testing this hypothesis. Although masking by object substitution was observed, it did not interact with the AB. An alternative hypothesis is proposed stating that mostly early-stage visual processes mediate the masking effects that are critical to the AB.     

The information for catching fly balls: judging and intercepting virtual balls in a CAVE

Visually guided action implies the existence of information as well as a control law relating that information to movement. For ball catching, the Chapman Strategy--keeping constant the rate of change of the tangent of the elevation angle (d(tan(alpha))/dt)--leads a catcher to the right location at the right time to intercept a fly ball. Previous studies showed the ability to detect the information and the consistency of running patterns with the use of the strategy. However, only direct manipulation of information can show its use. Participants were asked to intercept virtual balls in a Cave Automated Virtual Environment (CAVE) or to judge whether balls would pass behind or in front of them. Catchers in the CAVE successfully intercepted virtual balls with their forehead. Furthermore, the timing of judgments was related to the patterns of changing d(tan(alpha))/dt. The advantages and disadvantages of a CAVE as a tool for studying interceptive action are discussed.     

Surveying a blank field with the attentional spotlight

Spatial localization is a unique aspect of selective attention that precedes and facilitates other aspects of sensory processing. A common model of spatial attention is an attentional spotlight that enlarges to fit attentional demands. It is unclear if this attentional spotlight expands to survey a blank field or to scan the spatial environment with a smaller attentional spotlight. Two tachistoscopic experiments with young adults investigated how attention is surveyed in a blank field. Exp. 1 consisted of single letters at two concentric regions and under different conditions of attentional demand. Reaction times were proportionally slower for stimuli occurring in a combination of the two regions located at different distances from the fixation point than for stimuli occurring in each region alone. This finding is not consistent with attentional spread to encompass the entire attentional field. The addition of more stimulus locations within each single region yielded significantly slower reaction times. Together these findings suggest that a small attentional spotlight serially monitors different regions of the visual field when there are anticipated locations to be attended.     

Subfactors of DSM-IV Conduct Disorder: Evidence and Connections with Syndromes from the Child Behavior Checklist

Is conduct disorder (CD) as defined in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; American Psychiatric Association, 1994) a unitary entity, or do variants of CD exist? We addressed this question, using data collected from the parents of 1,669 Australian boys, aged 6–17. Parents were interviewed to assess DSM-IV Conduct Disorder (DSM-IV CD) criteria. Results revealed 2 subfactors of DSM-IV CD symptoms, made up of overt behaviors (e.g., initiating physical fights) and covert behaviors (e.g., stealing without confrontation). Ordinary least squares regressions showed the 2 CD subfactors to be significantly and uniquely predicted by Child Behavior Checklist (CBCL; T. M. Achenbach, 1991a, 1991b) syndromes labeled Aggressive Behavior and Delinquent Behavior, respectively. The results are discussed in terms of the utility of differentiating these 2 variants of CD in future editions of the DSM.     

Cortical morphology associated with language function in neurofibromatosis,type I

Neurofibromatosis, type I (NF-I) is associated with verbal and nonverbal neuropsychological deficits and neuroanatomical anomalies. Few relationships between CNS abnormalities and cognitive function in this population, however, have been found. Reading disabilities and developmental language impairments in the general population have been associated with particular morphologic features in inferior frontal gyrus (IFG) and Heschl's gyrus (HG). We compared the morphology of these regions in children with NF-I and controls. Verbal skills in NF-I were related to IFG morphology, such that individuals with NF-I who showed "typical" gyral patterns in the right hemisphere performed worse across language measures than those showing an extra "atypical" gyrus. A doubling of HG in the left and right hemispheres was also significantly associated with performance on several neuropsychological measures. This is the first study to link regional gyral morphology with language function in NF-I. A possible molecular basis for the observed relationships is discussed.     

Cerebral blood flow and anxiety in older men: an analysis of resting anterior asymmetry and prefrontal regions

Asymmetric resting blood flow in prefrontal and hemispheric regions, assessed by single photon emission computed tomography (SPECT), was examined as a potential biological marker for enhanced trait and state anxiety in 30 older men (ages 55-81). Average and asymmetric perfusion in dorsolateral, medial, and orbital regions of the prefrontal lobes was also assessed. Results indicated a significant association between lower levels of resting dorsolateral blood flow and greater state anxiety responses to a series of stressful provocations (measured on a separate occasion). A significant curvilinear (U-shaped) relation between asymmetric dorsolateral perfusion and state anxiety was also identified; increased asymmetric blood flow favoring either the right or the left dorsolateral region related to higher levels of state anxiety. However, this association was attenuated by age and systolic blood pressure. Resting perfusion in the dorsolateral region may represent a more reliable biological marker for state anxiety than trait anxiety in older men.     

Visual identification and spatial location in Alzheimer's disease

Twelve patients with Alzheimer's disease (AD) and 15 healthy elderly control subjects were shown sets of luminance-defined letters, texture-defined letters, luminance-defined squares, and texture-defined squares. They were asked to name the letters or point to the target square on each page. The stimuli were graded into four levels of difficulty based on the amount of contrast between the figure and the background. Performance was measured in terms of the maximum level of difficulty at which the participant correctly identified or located the three figures. Contrary to expectations, no significant difference was found between the performance of AD patients and control subjects on texture discrimination tasks vs. luminance discrimination tasks. However, results indicate that AD patients are impaired in performing a task requiring them to locate a texture-defined target of known shape in a noisy background field. By contrast, AD patients show no significant deficit in a task requiring them to locate a texture-defined shape in a known location. This argues that the observed deficit in the location task is not due to a failure in the system that discriminates target texture from background texture (since both location and identification tasks require the same textural discriminations), but rather to an impairment of the system responsible for "finding things" (i.e., locating known targets at unknown locations). This observation suggests that AD patients may suffer selective damage to the dorsal "Where" pathway, which is responsible for localizing objects in space.