A Search for the Optimal Stimulus

How do stimulus size and item number relate to the magnitude and direction of error on center estimation and line cancellation tests? How might this relationship inform theories concerning spatial neglect? These questions were addressed by testing twenty patients with right hemisphere lesions, eleven with left hemisphere lesions and eleven normal control subjects on multiple versions of center estimation and line cancellation tests. Patients who made large errors on these tests also demonstrated an optimal or pivotal stimulus value, i.e., a particular size center estimation test or number of lines on cancellation that either minimized error magnitude relative to other size stimuli (optimal) or marked the boundary between normal and abnormal performance (pivotal). Patients with right hemisphere lesions made increasingly greater errors on the center estimation test as stimuli were both larger and smaller than the optimal value, whereas those with left hemisphere lesions made greater errors as stimuli were smaller than a pivotal value. In normal subjects, the direction of errors on center estimation stimuli shifted from the right of true center to the left as stimuli decreased in size (i.e., the crossover effect). Right hemisphere lesions exaggerated this effect, whereas left hemisphere lesions diminished and possibly reversed the direction of crossover. Error direction did not change as a function of stimulus value on cancellation tests. The demonstration of optimal and pivotal stimulus values indicates that performances on center estimation and cancellation tests in neglect are only relative to the stimuli used. In light of other studies, our findings indicate that patients with spatial neglect grossly overestimate the size of small stimuli and underestimate the size of large stimuli, that crossover represents an “apparent” shift in error direction that actually results from normally occurring errors in size perception, and that the left hemisphere is specialized for one aspect of size estimation, whereas the right performs dual roles.     

Aspects of biochemical differentiation in the central nervous system

A demonstration of cell-specific patterns of development in the immature CNS is provided by examples of characteristic, cellspecific time-courses of enzyme development in different classes of brain cells isolated in highly purified form by bulk-separation from the cerebral and cerebellar cortex of the growing rat. The enzymatic analysis was carried out at the level of the nerve and glial cell lysosomes and mitochondria, two subcellular organelles crucial to the economy of all cells. The findings reveal rather similar developmental patterns for the lysosomal hydrolase N-acetyl-β-D-glucosaminidase in neurons and glial cells of the cerebral cortex as well as in two different cerebellar nerve cell types, the Purkinje and the granule cell. However, significant differences in the post-natal chronology of development of the mitochondrial enzyme α-glycerophosphate dehydrogenase were noted between cortical nerve and glial cells, the glial enzyme exhibiting 6-fold higher levels of activity than the neuronal one throughout the first month of postnatal life. The findings emphasize the feasibility as well as the necessity of studies aimed at the elucidation of the cell-specific aspects of the biochemistry of developing nerve and glial cells.     

Operating characteristic analysis of attribute ratings

The analysis of receiver operating characteristics as employed in psychophysics is suggested as a way of obtaining several useful measures in the context of attribute ratings. These include the difference between two stimuli on the attribute, the tendency for Ss to favor one pole of the rating scale, width of rating categories, and equal interval properties of the rating scale. The underlying measurement model is described along with means of evaluating its basic assumptions.     

Enactive imagery in paired-associate learning

Three experiments were conducted to study the effects of enactive imagery (EI) on associative learning. In Experiment I, groups of Ss rated 226 verbs on EI and frequency. In Experiments II and III, Ss learned a 24- and a 16-item list, respectively. The lists consisted of the four possible stimulus-response combinations of high (H) and low (L) EI verb pairs: H-H, H-L, L-H, L-L. In both experiments, EI was found to be a significant factor on the stimulus side, performance being superior when the stimulus was of high EI. In Experiment III, the response EI main effect and the Stimulus by Response EI interaction were also found to be significant. The results indicated that like the imagery evoked by nouns, the EI evoked by verbs facilitates learning.     

Adaptation effects on evoked electrical taste

In spite of a clear increment in absolute thresholds as an effect of self-adaptation, the electrically provoked taste sensation does not show a reduction in subjective intensity during the protracted stimulation time. Chemical cross-adaptation effects on the threshold and suprathreshold levels of electrical taste are observed only when the adapting solutions are electrolytes regardless of their taste qualities. It seems that the stability of perceived intensity during current flow is principally due to some irritation of the sensitive tissue of the tongue, whereas cross-adaptation effects may be attributed to the potential changes across the excitable membranes caused by electrical properties of adapting electrolytic solutions.     

Pop-out and pop-in: Visual working memory advantages for unique items

Attentional control is thought to play a critical role in determining the amount of information that can be stored and retrieved from visual working memory (VWM). We tested whether and how task-irrelevant feature-based salience, known to affect the control of visual attention, affects VWM performance. Our results show that features of a task-irrelevant color singleton are more likely to be recalled from VWM than non-singleton items and that this increased memorability comes at a cost to the other items in the display. Furthermore, the singleton effect in VWM was negatively correlated with an individual’s baseline VWM capacity. Taken together, these results suggest that individual differences in VWM storage capacity may be partially attributable to the ability to ignore differences in task-irrelevant physical salience.     

Differences in the micromechanical properties of dendrites and interdendritic regions in superalloys

Statistical analysis of white-light interferometry (WLI) experiments performed on Ni-based single-crystal superalloys (SX) have revealed a different height distribution between the dendritic cores (DCs) and the interdendritic regions (IRs) of the polished samples. The micromechanical property difference is largely ascribed to the uneven distribution of the alloying elements. In this context, possible reasons for this difference are discussed by comparing with different experiment results obtained by previous researchers, and a proposal forecasting the hardness ratio of IRs/DCs is put forward.     

Case illustration: Moving along…and,is change gradual or sudden?

A sequence of analytic sessions of a professional woman in her forties is used to illustrate the moving along process. The material shows a gradual change, where the patient's experience of her sense of agency is altered through a particular kind of interactive sequence. The example is intended to make it clear that the group's view of how change occurs is not strictly or primarily in terms of sudden changes, and that the problem of assessing moments of meeting as well as quantitative and qualitative shifts is one with which the group continues to struggle. © 1998 Michigan Association for Infant Mental Health