The perceived strength of illusory contours

Illusory contours are not well understood, partially because a lack of physical substance complicates their specification via physical standards. One solution is to gauge illusory contours with respect to luminance-defined contours, which are easily quantified physically. Accordingly, we chose a metric (perceived contrast) that expresses illusory contour strength in terms of the physical contrast of luminance-defined contours. Using this metric, adult observers adjusted the contrast of a luminance-defined contour until it matched the perceived contrast of an illusory contour. Illusory contour length, inducer size, and inducer contrast all influenced illusory contour strength.. The results are adequately explained via low-level visual processes. It appears that matching paradigms can be beneficial in quantitative studies of illusory contours.     

Selective attention to specific location cues: the peak and center of a patch are equally accessible as location cues.

Asymmetric patterns have several spatially distinct cues for spatial localization. These cues include the peak of the luminance distribution, the centroid of the contrast distribution, zero-crossings in the second derivative of the luminance profile, and the midpoint of the visible area. If these cues are represented as primitives in the visual system, the observer should be able to access them at will. To examine whether observers can selectively attend to particular cues, we measured perceived alignment for an asymmetric pattern with two distinct instructions: "align the peak", and "align the center". We found that observers could align the patterns in accord with the instructions with identical precision, suggesting that the peak and the center cues were equally accessible by the observer. We conclude that multiple localization cues are represented in and can be selectively accessed by the visual system.     

Posttraumatic stress symptoms in children following orthopedic or traumatic brain injury.

Examined posttraumatic stress (PTS) symptoms in children following pediatric traumatic brain injury (TBI). Children (ages 6-12) with TBI (n = 81) and orthopedic injury (OI; n = 59) were assessed 6 and 12 months postinjury. Parents of children with severe TBI reported higher levels of child PTS symptoms than did parents of children with moderate TBI or OI at the 6- and 12-month follow-ups. Group differences in child-reported PTS symptoms emerged at the 12-month follow-up with higher symptom levels reported by children with severe TBI than by those with moderate TBI or OI. At both follow-ups, rates of clinically significant symptom levels were higher in the severe TBI group than in the moderate TBI or OI groups. The group differences in parent and child reports were significant even after taking ethnicity, social disadvantage, and age at injury into account. Parent and child reports of child PTS symptoms were related to family socioeconomic status. Implications for clinical intervention with children and families following pediatric TBI are discussed.     

Replies to Comesaña and Yablo

There are few indulgences academics can crave more than to have their work considered and addressed by leading researchers in their field. We have been fortunate to have two outstanding philosophers from whose work we have learned a great deal give ours their thoughtful attention. Grappling with Stephen Yablo’s, and Juan Comesaña’s comments and criticisms has helped us gain a better understanding of our ideas as well as their shortcomings. We are extremely grateful to them for the attentiveness and seriousness with which they have considered our arguments and to philosophical studies for giving us this opportunity. Given the substantive difference between the two response papers, there is not much beyond sincere gratitude that we can covey to them jointly. We will therefore address them in turn.     

Counterexamples to Recovery and the Filtering Condition

David Makinson has argued that the compelling character of counterexamples to the Recovery Condition on contraction is due to an appeal to justificational structure. In “naked theories” where such structure is ignored or is not present, Recovery does apply. This note attempts to show that Makinson is mistaken on both counts. Recovery fails when no appeal is made to justificational structure. This revised version was published online in August 2006 with corrections to the Cover Date.