Biomedical subjects

L A Carlson-Radvansky

Publications and source records attributed to L A Carlson-Radvansky.

5 recordsLinked to original sources

PubMed2000

Functional influences on orienting a reference frame.

Spatial relational terms like above are defined with respect to a reference frame. Reference frames are imposed on reference objects and define the space in which to search for a located object. Reference frames have a number of parameters that must be set during spatial term assignment, including origin, scale, and orientation. Previous research has shown that a functional relationship between objects in the scene influences the selection of a reference frame (Carlson-Radvansky & Radvansky, 1996). However, because this work operated at the level of the reference frame, generalizing across various spatial terms, it is unclear how function had its influence. One possibility is that function influences how the parameters of a reference frame are set. Consistent with this idea, Carlson-Radvansky, Covey, and Lattanzi (1999) showed an influence of function on where the origin of a reference frame was imposed. The present paper demonstrates that function also influences how the orientation of the axes of a reference frame is set. The implications for setting multiple parameters of a reference frame are discussed.

Humans↗

PubMed2000

The role of the saccade target object in the perception of a visually stable world.

Although the proximal stimulus shifts position on our retinae with each saccade, we perceive our world as stable and continuous. Most theories of visual stability implicitly assume a mechanism that spatially adjusts perceived locations associated with the retinal array by using, as a parameter, extra-retinal eye position information, a signal that encodes the size and direction of the saccade. The results from the experiment reported in this article challenge this idea. During a participant's saccade to a target object, one of the following was displaced: the entire scene, the target object, or the background behind the target object. Participants detected the displacement of the target object twice as frequently as the displacement of the entire background. The direction of displacement relative to the saccade also affected detectability. We use a new theory, the saccade target theory (McConkie & Currie, 1996), to interpret these results. This theory proposes that retinal (as opposed to extra-retinal) factors, primarily those concerning the saccade target object, are critical for the detection of intrasaccadic stimulus shifts.

Fixation, Ocular↗

PubMed1999

Memory for relational information across eye movements.

Structural descriptions are hierarchical representations of a visual stimulus in terms of its parts and their relations. Previous research in which the retention of parts was examined has shown that structural descriptions can be used to represent information in transsaccadic memory. In three experiments, this idea was tested further by examining whether relational information is also maintained across saccades. Experiment 1, in which a same/different comparison task was used, showed that both part and relation information are retained across fixations in the same manner as within a fixation. Experiment 2 showed that such retention is impervious to instruction. Finally, Experiment 3, in which a new set of stimuli was used, demonstrated that both coordinate and categorical relations are maintained across saccades. The results indicate that structural descriptions can be used to represent information in transsaccadic memory in a manner similar to their use in visual short-term memory.

Fixation, Ocular↗

PubMed1995

Uncertainty in estimating distances from memory.

Magnitude estimations involving spatial characteristics, such as distance, typically show a compressive function when estimates are made from memory. In particular, as the magnitude of a property grows larger and larger, estimates become more and more inaccurate, with increasing underestimates of the actual magnitude. Previous theories have attempted to explain this difference by supposing that magnitude estimation was accomplished through a reperceptual process, in which the errors of perception are magnified, or a transformation process, in which the memory trace undergoes a consistent alteration toward a more schematic form. The present experiments present evidence in support of an uncertainty hypothesis. When subjects are uncertain of the actual value of a distance, they are forced to guess on the basis of the mean distance they encountered, because they are unable to retrieve the information accurately. When they can retrieve the information, they are more certain and their estimates are more accurate. This hypothesis was also extended to integrative conditions in which the subjects were presented with the stimulus display in a piecemeal fashion. In these cases, distance estimates were derived by combining spatial representations. This method of presentation caused distance estimates to become less accurate.

Attention↗

PubMed1993

Frames of reference in vision and language: where is above?

Spatial terms such as "above" must be used and interpreted with respect to some frame of reference. Perceptual cues for verticality were varied in four experiments to investigate whether the comprehension and production of "above" is based on a viewer-centered (deictic) frame, an environment-centered (extrinsic) frame, or an object-centered (intrinsic) frame of reference. "Above" was usually interpreted with respect to an environment-centered reference frame, but there was a significant contribution from object-centered reference frames as well; the viewer-centered reference frame made no independent contribution to "above". The meaning of "above" appears not to specify a particular reference frame; rather, selection of a reference frame during spatial assignment determines how spatial terms such as "above" and "below" will be used and interpreted.

Adult↗