Search PubMed⌕ Search

Biomedical subjects

J T Todd

Publications and source records attributed to J T Todd.

59 records · Page 4Linked to original sources
PubMed1981

Perception of growth: a geometric analysis of how different styles of change are distinguished.

Although there have been many demonstrations that human observers can accurately recognize a variety of styles of change, such as rolling, walking, or growing, there are no existing theories capable of explaining how one style of change is distinguished from another. The present article offers a hypothesis that any recognizable style of change is uniquely specified by geometric invariants- the abstract properties of a visual display that are preserved by the change. In an effort to provide an empirical test of this hypothesis, several experiments involving the perception of growth were performed. Observers were required to make perceptual judgments of consequences of facial profiles, each of which was constructed by using a different mathematical transformation. The same pattern of results was obtained on both a free response task and a growth rating task: All transformations that were consistently identified as growth preserved the same geometric invariants.

Adolescent↗
PubMed1981

Visual information about moving objects.

A mathematical model of visual flow is presented, which could potentially account for an observer's ability to effectively interact with moving objects. The analysis demonstrates that there is visual information available to an observer about (a) a moving object's angle of approach, (b) changes in its velocity and acceleration, (c) whether its velocity and acceleration are positive or negative, (d) its time to collision with both the horizontal and vertical axes, and (e) whether it will cross the horizontal axis in front of or behind the point of observation. Several experiments are reported in which observer's sensitivity to these different aspects of visual information is examined using a variety of experimental tasks. The results suggest that human observers are highly sensitive to many abstract properties of visual stimulation, but that they are not sensitive to all of the information that is potentially available.

Discrimination, Psychological↗
PubMed1979

Implications of a transient-sustained dichotomy for the measurement of human performance.

Recent evidence suggests that the human visual system has two components: a sustained system that will respond to static contrasts and a transient system that will only respond to rapid changes over time. The present article provides further support for a transient-sustained dichotomy of visual information processing by examining the effects of abrupt changes in visual stimulation in a variety of situations. Several experiments are reported in which stimuli are presented both with and without abrupt onsets. The results of these experiments, together with other evidence, suggest that the overall effects of abrupt changes in visual stimulation may be more extensive than has previously been suspected.

Cues↗