Biomedical subjects

William L Thompson

Publications and source records attributed to William L Thompson.

4 recordsLinked to original sources

PubMed2003

Implicit transfer of motor strategies in mental rotation.

Recent research indicates that motor areas are activated in some types of mental rotation. Many of these studies have required participants to perform egocentric transformations of body parts or whole bodies; however, motor activation also has been found with nonbody objects when participants explicitly relate the objects to their hands. The current study used positron emission tomography (PET) to examine whether such egocentric motor strategies can be transferred implicitly from one type of mental rotation to another. Two groups of participants were tested. In the Hand-Object group, participants performed imaginal rotations of pictures of hands; following this, they then made similar judgments of pictures of Shepard-Metzler objects. The Object-Object group performed the rotation task for two sets of Shepard-Metzler objects only. When the second condition in each group (which always required rotating Shepard-Metzler objects) was compared, motor areas (Area 6 and M1) were found to be activated only in the Hand-Object group. These findings suggest that motor strategies can be covertly transferred to imaginal transformations of nonbody objects.

Adolescent↗

PubMed2003

Visual imagery in cerebral visual dysfunction.

Many sorts of deficits in imagery follow brain damage, but the relation between the site of damage and the type of deficit is not simple or straightforward. The dissociations in performance after brain damage provide hints regarding the processing system underlying imagery, but difficulties in interpretation urge caution in mapping these findings to theoretic models. Neuroimaging techniques, such as PET and fMRI, open a window into the working brain and offer valuable information not easily accessible through the study of patients, who, as noted, may have deficits beyond those observable and may rely on compensation and neural reorganization. As we come to understand the mental imagery system more fully, such issues as the laterality of image generation are likely to prove too coarse and vague. The brain is an enormously intricate organ, and even within a circumscribed domain such as imagery it seems to process information in complex and subtle ways.

Functional Laterality↗

PubMed2003

When is early visual cortex activated during visual mental imagery?

Although many neuroimaging studies of visual mental imagery have revealed activation in early visual cortex (Areas 17 or 18), many others have not. The authors review this literature and compare how well 3 models explain the disparate results. Each study was coded 1 or 0, indicating whether activation in early visual cortex was observed, and sets of variables associated with each model were fit to the observed results using logistic regression analysis. Three variables predicted all of the systematic differences in the probability of activation across studies. Two of these variables were identified with a perceptual anticipation theory, and the other was identified with a methodological factors theory. Thus, the variability in the literature is not random.

Humans↗

PubMed2002

Visual cortex excitability increases during visual mental imagery--a TMS study in healthy human subjects.

Previous neuroimaging studies provided evidence that visual mental imagery relies, in part, on the primary visual cortex. We hypothesized that, analogous to the finding that motor imagery increases the excitability of motor cortex, visual imagery should increase visual cortex excitability, as indexed by a decrease in the phosphene threshold (PT). In order to test visual cortex excitability, the primary visual cortex was stimulated with transcranial magnetic stimulation (TMS), so as to elicit phosphenes in the right lower visual quadrant. Subjects performed a visual imagery task and an auditory control task. We applied TMS with increasing intensity to determine the PT for each subject. Independent of the quadrant in which subjects placed their visual images, imagery decreased PT compared to baseline PT; in contrast, the auditory task did not change PT. These findings demonstrate for the first time a short-term, task-dependent modulation of PT. These results constitute evidence that early visual areas participate in visual imagery processing.

Adult↗