Spatial localization of warmth

This study explored the ability to localize warmth sensations produced by radiant stimulation of the forearm. The subject’s task was to state on which side of a tactile reference line warmth was perceived. Percentage correct improved with increasing intensity of the radiation, as well as with increasing distance from the reference line. There appears to be an inverse relation between the ability to make spatial judgments and the degree of spatial summation. At low levels of stimulation, intensity and area both contribute heavily to the magnitude of a warmth sensation and spatial localization is poor; but with increasing level, area contributes less and less to sensation and localization is better.     

Spatial summation and the dynamics of warmth sensation

Various areal extents of the forehead and back were thermally irradiated at various levels of intensity. For any areal extent, the degree of apparent warmth grows approximately as a power function of intensity level; the larger the area, the smaller the exponent of the power function. Two families of psychophysical functions, one for the forehead, the other for the back, both show that the power functions extrapolate to a point of convergence in the neighborhood of the threshold for pain and tissue impairment. The rules that govern spatial summation of warmth reveal themselvesin the two families. Intensity and area trade one for the other to preserve the same level of warmth. At faint sensation levels, reciprocity is the rule of trading; but with increasing sensation level, area makes a weaker and weaker relative contribution to warmth, and, as a result, it takes a larger and larger percentage change in area to offset a given percentage change in intensity.     

Spatial frequency discrimination in schizophrenia

Pathways within the visual system can be distinguished on the basis of selectivity for low or high spatial frequencies. Spatial frequency discrimination was evaluated in 17 medicated male patients with schizophrenia and 19 male control subjects. Subjects were required to discriminate whether pairs of high contrast, sinusoidally modulated gratings were the same or different in spatial frequency. Accuracy performance was compared at high, medium, and low spatial frequencies on tasks matched for control performance. Patients showed a greater performance decrement of 12% on low as compared with 4% on high spatial frequencies. These findings suggest a disturbance of right hemisphere mechanisms involved in spatial perception and attention in schizophrenia.     

Spatial attention does improve temporal discrimination

It has recently been stated that exogenous attention impairs temporal-resolution tasks (Hein, Rolke, & Ulrich, 2006; Rolke, Dinkelbach, Hein, & Ulrich, 2008; Yeshurun, 2004; Yeshurun & Levy, 2003). In comparisons of performance on spatially cued trials versus neutral cued trials, the results have suggested that spatial attention decreases temporal resolution. However, when performance on cued and uncued trials has been compared in order to equate for cue salience, typically speed—accuracy trade-offs (SATs) have been observed, making the interpretation of the results difficult. In the present experiments, we aimed at studying the effect of spatial attention in temporal resolution while using a procedure to control for SATs. We controlled reaction times (RTs) by constraining the time to respond, so that response decisions would be made within comparable time windows. The results revealed that when RT was controlled, performance was impaired for cued trials as compared with neutral trials, replicating previous findings. However, when cued and uncued trials were compared, performance was actually improved for cued trials as compared with uncued trials. These results suggest that SAT effects may have played an important role in the previous studies, because when they were controlled and measured, the results reversed, revealing that exogenous attention does improve performance on temporal-resolution tasks.     

Spatial coding and oblique discrimination by children

Children from five to eight years of age learned to discriminate between mirrorimage oblique lines more readily when cards bearing the obliques were presented vertically than when they were presented horizontally. The difference in performance between the vertical and horizontal planes could not be accounted for by differences in either the external visual context or the availability of asymmetrical body information (e.g., left vs right hand). The superiority of the vertical plane was attributed to the congruence of objective, bodily, and retinal vertical axes for the vertical, but not the horizontal plane, It was concluded, on this basis, that at least part of children's difficulty discriminating between mirror-image obliques is due to their difficulty establishing the internalized vertical axis necessary for the left-right spatial coding of the obliques.     

Spatial numerosity discrimination as contingent upon sensory and extrinsic factors

Stimulus value, number, and exposure time were varied systematically to determine their joint and independent effects on number discrimination. It was concluded that stimulus value can function to alter immediate estimations of spatial number but that mediational counting and sensory subitizing of patterns are unaffected.     

Spatial contrast sensitivity does not explain random figure discrimination latency

Both humans and other mammals can more easily discriminate eight-sided figures from one another than they can figures having more or fewer sides. The hypothesis that this effect is based upon spatial contrast sensitivity was tested by varying viewing distance and hence spatial frequency content. Because viewing distance had tittle effect upon relative discrimination latency, it was concluded that the superior discriminability of eight-sided figures is not based upon spatial contrast sensitivity. The possibility that orientation tuning of visual cortex neurons may account for the effect is discussed.     

Temporal summation at the warmth threshold

Threshold levels for warmth aroused by infrared irradiation were measured in sLx Ss at durations between 0.05 and 10 sec. Beyond a critical duration of about a second, the threshold does not depend on duration. Below critical duration time t trades for irradiance ? by the formula ? = kt^?0.82. That these properties do not depend much on areal extent of stimulation was demonstrated by a study that compared temporal summation for two different areas of the same S’s skin. Individual differences in apparent absolute sensitivity were explored under the rubric of the theory of signal detection.     

Spatial coherence does not affect contrast discrimination for multiple Gabor stimuli

Gestalt grouping rules imply a process or mechanism for grouping together local features of an object into a perceptual whole. Several psychophysical experiments have been interpreted as evidence for constrained interactions between nearby spatial filter elements and this has led to the hypothesis that element linking might be mediated by these interactions. A common tacit assumption is that these interactions result in response modulation which disturbs a local contrast code. We addressed this possibility by performing contrast discrimination experiments using two-dimensional arrays of multiple Gabor patches arranged either (i) vertically, (ii) in circles (coherent conditions), or (iii) randomly (incoherent condition), as well as for a single Gabor patch. In each condition, contrast increments were applied to either the entire test stimulus (experiment 1) or a single patch whose position was cued (experiment 2). In experiment 3, the texture stimuli were reduced to a single contour by displaying only the central vertical strip. Performance was better for the multiple-patch conditions than for the single-patch condition, but whether the multiple-patch stimulus was coherent or not had no systematic effect on the results in any of the experiments. We conclude that constrained local interactions do not interfere with a local contrast code for our suprathreshold stimuli, suggesting that, in general, this is not the way in which element linking is achieved. The possibility that interactions are involved in enhancing the detectability of contour elements at threshold remains unchallenged by our experiments.     

Spatial and non-spatial visual discrimination learning in zebrafish (Danio rerio)

Zebrafish (Danio rerio) provide an excellent model for assessment of molecular processes of neurodevelopment. To determine the functional importance of molecular events during neurodevelopment, we have developed methods for assessing learning in zebrafish in a three-chambered fish tank. In the first study, simple escape response was assessed. Zebrafish tested with a moving net learned to escape to another chamber more rapidly over the six sessions of training than the fish with the still net which did not learn. Upon reversal of the contingencies, the fish switched to the inactive net rapidly learned to suppress the escape response and fish formerly in the inactive net condition learned to avoid the moving net. In the second study, spatial discrimination learning was assessed. Zebrafish were trained on a right-left position discrimination to avoid the active net. Zebrafish showed significant improvement in escape responses over six sessions of training with three trials per session. In the third study, red-blue non-spatial discrimination learning was assessed. There was a significant improvement over the first six training sessions. With the reversal of contingencies, there was a significant decline of performance. With continued training, the fish again significantly improved avoidance. These studies found an effective motivational stimulus and procedure for studying escape behavior in zebrafish; a procedure whereby zebrafish would learn both spatial and non-spatial discrimination. These methods are being developed to help determine the functional importance of molecular events during zebrafish neurodevelopment. Accepted after revision: 20 August 2001 Electronic Publication     

Apparent warmth as a function of thermal irradiation

The skin of the back was periodically exposed to a source of radiant heat. In Experiment 1, 20 Ss matched numbers to the apparent warmth aroused by various levels of irradiant flux (method of magnitude estimation). In Experiment 2, 15 Ss matched the loudness of a white noise to the apparent uwmth aroused by the same levels used in Experiment I (method of cross-modality matching). Both experiments showed that apparent warmth is related to absorbed irradiance by a power function whose exponent is approximately 0.7.     

Personal warmth and psychological health at midlife

Personal warmth, arguably a strong trait in the makeup of psychological health, seems to fade in conceptual importance at midlife. In contrast, ideas of interiority and androgyny appear to gain conceptual importance at midlife. The present study sought to rebalance these foci by determining the predictive power of personal warmth for psychological health of men and women at age 50: first, by developing separate California Psychological Inventory (CPI) scales to assess personal warmth; next, by joining these warmth scales with the 20 standard CPI scales to predict psychological health. Without the personal warmth scale, the standard CPI scales do not significantly predict psychological health for men; for women, the standard scales do. For both genders, the personal warmth scales add significantly to the predictability of psychological health. The results point to an amendment of current theoretical formulations of interiority and androgyny to better understand optimal psychological development in men and women at midlife.     

Reaction time as a measure of summation of warmth

Reaction time (RT) to radiant heat applied to the forehead and to the back was found to decrease monotonically as a function of two variables: intensity (flux density) and areal extent of stimulation. Intensity and area can thus be traded one for the other to preserve a constant RT. It has previously been shown that intensity and area can be traded to preserve a constant degree of apparent warmth, as determined by magnitude estimation. RT and magnitude estimation therefore agree in showing that the warmth sense displays spatial summation, and both show that summation is very great. They also agree in showing that the foreheadés sensitivity greatly exceeds the backés, and the exact trading rules revealed by magnitude estimation and RT agree well at low and moderate intensities.