Biomedical subjects

D H Arnold

Publications and source records attributed to D H Arnold.

6 recordsLinked to original sources

PubMed2001

Asynchronous processing in vision: color leads motion.

It has been demonstrated that subjects do not report changes in color and direction of motion as being co-incidental when they occur synchronously. Instead, for the changes to be reported as being synchronous, changes in direction of motion must precede changes in color. To explain this observation, some researchers have suggested that the neural processing of color and motion is asynchronous. This interpretation has been criticized on the basis that processing time may not correlate directly and invariantly with perceived time of occurrence. Here we examine this possibility by making use of the color-contingent motion aftereffect. By correlating color states disproportionately with two directions of motion, we produced and measured color-contingent motion aftereffects as a function of the range of physical correlations. The aftereffects observed are consistent with the perceptual correlation between color and motion being different from the physical correlation. These findings demonstrate asynchronous processing for different stimulus attributes, with color being processed more quickly than motion. This suggests that the time course of perceptual experience correlates directly with that of neural activity.

Color Perception↗

PubMed2001

Orthogonal adaptation improves orientation discrimination.

We investigated the effect of adaptation on orientation discrimination using two experienced observers, then replicated the main effects using a total of 50 naïve subjects. Orientation discrimination around vertical improved after adaptation to either horizontal or vertical gratings, but was impaired by adaptation at 7.5 or 15 degrees from vertical. Improvement was greatest when adapter and test were orthogonal. We show that the results can be understood in terms of a functional model of adaptation in cortical vision.

Adaptation, Physiological↗

PubMed2000

Dissociable factors affect speed perception and discrimination.

Factors affecting our judgement of the speed of visual motion were investigated. Two types of judgement were made: perceived speed relative to a standard comparison stimulus, and discrimination between the speeds of similar stimuli. The factors affect ng these two judgements were found to be doubly dissociable, suggesting that they may be constrained by processing at different levels of the visual hierarchy. The results are discussed in terms of the 3-D interpretation of visual image motion, and related to possible neural substrates.

Humans↗

PubMed1999

Effects of environmental factors on development of wood.

This research tested the hypothesis that environmental factors (light, water, and nutrient levels) affect wood development. Specimens were placed in treatments of low, medium, or high levels of light, water, nitrogen, or phosphorus for one year. Control plants received medium levels of all factors, while experimental plants received medium levels of all factors except the experimental factor; for example, "high light" treatment consisted of high light but medium levels of water, nitrogen, and phosphorus. Some character changes seen in Cereus peruvianus were a reduction in mean vessel diameter and shoot elongation as a result of low nitrogen and low phosphorus treatments and a reduction in mean vessel density due to low light; high water induced broader vessels and greater shoot elongation. In Cereus tetragonus, low water treatment caused a reduction in mean vessel diameter, and high nitrogen decreased the amount of wood produced. Whereas all characters studied showed a significant correlation with at least one treatment in one species, few characters responded similarly between species. Estimated specific conductivity of wood could be altered by treatments affecting either vessel density or vessel diameter strongly or by treatments affecting both diameter and density weakly. Under the conditions tested, wood structure was stable but estimated conducting capacity was more flexible.

Journal Article↗

PubMed1998

Teacher discipline and child misbehavior in day care: untangling causality with correlational data.

Day-care centers provide an ideal, underused setting for studying the developmental processes of child psychopathology. The influence of day-care teachers' lax and overreactive discipline on children's behavior problems was examined, as was the influence of children's behavior problems on teachers' discipline. Participants were 145 children and 16 day-care teachers from 8 classrooms in a day-care center for children from low-income families. Two techniques are presented for estimating causal relations based on correlational data gathered from day-care centers: 2-stage least squares and simultaneous structural equation modeling. Across techniques, teachers' laxness strongly influenced child misbehavior, and child misbehavior influenced both teachers' overreactivity and laxness. Teachers' overreactivity did not influence child misbehavior

Adult↗

PubMed1998

Data monitoring: a hypothesis-testing approach for treatment-outcome research.

Traditional inferential statistics require that hypotheses be evaluated at only 1 sample size. That is, researchers must choose how many participants will be included in a study before conducting analyses; they are not allowed to add data if initial results are not significant. This requirement forces researchers to choose among including more participants than necessary, risking inconclusive results, or violating the requirement by adding participants. This study presents a more flexible approach, called data monitoring, that allows repeating an analysis as the sample increases. First, the cost of the uncorrected data monitoring that researchers sometimes do is estimated. Second, the correction that is needed to allow data monitoring while holding an overall alpha at a desired level is estimated. Third, the power of data monitoring is compared with traditional approaches. This study also provides an example of the use of data monitoring. At least in some circumstances, data monitoring can reduce Type II error or the number of participants needed without sacrificing Type I error.

Animals↗