Orientation and luminance polarity tuning of the transient-vergence system.

Previously, Edwards, Pope & Schoor, Vision Research, 38, 705-717, demonstrated that transient disparity vergence appears to be mediated by a system that employs a single low-pass sensitive spatial channel whose performance is not reduced by dichoptic mixed contrasts (no contrast paradox) or dichoptic mixed spatial frequencies. This broadband tuning to both contrast and spatial frequency may be indicative of a second-order or non-linear envelope extraction system. The current study tests for lack of tuning to orientation and luminance polarity which are typically taken as evidence of a second-order system. We found that when the transient vergence system was simultaneously presented with both convergent and divergent disparities, there was a small but distinct bias in favor of responding in the direction defined by matched orientations or luminance polarities over unmatched pairs. Although less frequent, responses to orthogonal carriers or opposite luminance polarities were possible. The vergence system could match a horizontal with a vertical carrier, or a light gaussian with a dark gaussian. The degree of orientation or luminance polarity tuning varied inversely with the disparity magnitude over the range of 2.5-5 degrees, and the orientation tuning peaked at a spatial frequency about 2 cpd. At all disparities tested, however, the tuning was very broad, and other candidate features for mediating transient-vergence need to be investigated.     

Age-related changes in the kinetics of water transport in normal human lenses

The aim of this work was to study blink frequency changes and levels of ocular discomfort during work at a video display terminal, and the effects on these parameters of augmented or reduced humidification of the ocular surface.Blink rate was measured from recordings of the electrical signal evoked by the contraction of the orbicularis oculi muscle. Blink rate and interblink intervals were analyzed at rest and during performance of a task with a computer (playing a card game) for 10 or 30 min in steady environmental conditions and during application of a continuous stream of air to the face. In two separate sessions, the effect of pretreatment with humidifying ocular solutions of different elastoviscosity (balanced salt solution or elastoviscous 0.1% Hylan A solution) was assayed. At the end of each experimental period, the subjects marked the level of ocular discomfort experienced on a 0-10 cm visual analogue scale.The blink frequency at rest (12.4+/-1.2 blinks min-1) was reduced significantly (to 10.3+/-1.1 blinks min-1) by pretreatment with elastoviscous eyedrops both with and without air applied to the face. This effect was not obtained with balanced salt solution. During performance of the visual task for 10 or 30 min, basal blink rate decreased significantly, to about 40% of the control value. Neither application of an air jet on the face nor application of eye solutions of different viscosity modified this reduced blink rate.A low degree of ocular discomfort developed after performance of the visual task that was enhanced by air application to the face. This discomfort was reduced by pretreatment with ocular solutions, the elastoviscous eye solution being more efficient than the balanced salt solution. Interblink interval duration was also more regular after treatment with the elastoviscous solution.These data suggest that blink rate at rest is maintained in part by activation of sensory receptors of the cornea and conjunctiva, which are stimulated by desiccation of the ocular surface. Reduction of eye blink frequency elicited by the performance of a visual task with a computer appears to depend on central neural mechanisms that are quite independent of peripheral sensory inputs. The reduction of blink frequency consecutive to computer use was associated with a sensation of discomfort that was attenuated more effectively by elastoviscous eyedrops than by regular balanced salt solution.     

A pilot study of what African American maternal caregivers and their adolescent daughters talk about when asked to discuss tobacco together

Parents play a critical role in shaping their children’s substance use behaviors, yet few studies have examined the messages that caregivers give their adolescents about tobacco. In this study, we identify tobacco-related messages discussed by African American maternal caregivers and their adolescent daughters. Twenty-five African American maternal caregivers and their adolescent daughters participated in a video-taped discussion about tobacco. Discussions were transcribed and coded thematically. Seven themes emerged, which were grouped into tobacco-messages and communication strategies. Messages included health risks, non-health-related reasons to stop smoking, reasons people smoke, and tobacco products and marijuana. Strategies caregivers used to communicate their tobacco-related messages included sharing personal or their families’ experience with smoking, using humor, and role-playing. Finally, embedded within all of the themes, participants expressed their disapproval of tobacco use, whether it was directed at their own use, their adolescents’ use, a family members’ use, or peers’ use. African American maternal caregivers and their daughters openly talk about a variety of tobacco-related topics, and caregivers are open to sharing their own and their families’ experience with substance use. Findings also suggest that having caregivers and their adolescents participate in discussions tasks could be potentially beneficial in facilitating discussions and could identify areas in which caregivers could use help in discussing sensitive topics.