Two-point discrimination threshold is commonly used for assessing tactile spatial resolution. Since the effect of temporal features of cutaneous test stimulation on spatial discrimination ability is not yet well known, we determined whether the ability to discriminate between two stimulus locations varies with the interstimulus interval (ISI) of sequentially presented tactile stimuli or the length of the stimulus train. Electrotactile stimuli were applied to one or two locations on the skin of the thenar eminence of the hand in healthy human subjects. Tactile discrimination ability was determined using methods based on the signal detection theory allowing the assessment of sensory performance, independent of the subject's response criterion. With stimulus pairs, the ability to discriminate spatial features of stimulation (one location vs. two stimulus locations 4 cm apart) was improved when the ISI was equal to or longer than that required for tactile temporal discrimination. With stimulus trains, the ability to discriminate spatial features of stimulation was significantly improved with an increase in the stimulus train (from 3 to 11 pulses corresponding to train lengths from 40 to 200 ms). These results indicate that temporal features of tactile stimulation significantly influence sensory performance in a tactile spatial discrimination task. Precise control of temporal stimulus parameters should help to reduce variations in results on the two-point discrimination threshold.
This study, which focused on the validity of the SAT‐V and SAT‐M, used data from 99 validity studies that were conducted by the Validity Study Service of the College Board. In addition to test validities based on first‐year college averages, which were calculated using institutional data, validities for each college were also estimated for two other groups—applicants for admission to the colleges, and all SAT takers. These last two estimates were based on range restriction theory. Substantial validity generalization was found: the assumption that applicant pool validities were all equal, together with sampling variance and the effects of selection, accounted for 36 percent and 34 percent of the variation of the SAT‐V and SAT‐M validities, respectively. The hypothesis of equal validity in pools like those of all SAT takers, plus sampling variance and the effects of selection, accounted for 53 percent and 33 percent of the variation of the SAT‐verbal and SAT‐mathematical validities, respectively. However, significant institutional uniqueness remains, though part of that uniqueness consists of variation in the reliability of first‐year college average. For these data, substantial validity was the rule. The average validities were quite high, rising to .55 for either SAT‐V or SAT‐M true scores for all SAT takers, and 95 percent of the observed validities were above .13 for SAT‐V and .10 for SAT‐M. Values below these may be owing to accidents of sampling, computing errors, or criterion defects, and it should be noted that 95 percent is a conservative standard. Studies with slightly higher validities may be questioned as well, perhaps repeated, and the criterion examined carefully. A hypothesis that validities for SAT‐V and SAT‐M might differ across institutions but have the same ratio was also tested. It was thought that departures from this second assumption might lead to the detection of institutional types. However, significant departures from the equal‐ratio hypothesis tested at the 5 percent level occurred for about 5 percent of the institutions, so no detection of institutional types occurred.
To further the understanding how the human brain adapts to early-onset blindness, we searched in early-blind and normally-sighted subjects for functional brain networks showing the most and least spatial variabilities across subjects. We hypothesized that the functional networks compensating for early-onset blindness undergo cortical reorganization. To determine whether reorganization of functional networks affects spatial variability, we used functional magnetic resonance imaging to compare brain networks, derived by independent component analysis, of 7 early-blind and 7 sighted subjects while they rested or listened to an audio drama. In both conditions, the blind compared with sighted subjects showed more spatial variability in a bilateral parietal network (comprising the inferior parietal and angular gyri and precuneus) and in a bilateral auditory network (comprising the superior temporal gyri). In contrast, a vision-related left-hemisphere-lateralized occipital network (comprising the superior, middle and inferior occipital gyri, fusiform and lingual gyri, and the calcarine sulcus) was less variable in blind than sighted subjects. Another visual network and a tactile network were spatially more variable in the blind than sighted subjects in one condition. We contemplate whether our results on inter-subject spatial variability of brain networks are related to experience-dependent brain plasticity, and we suggest that auditory and parietal networks undergo a stronger experience-dependent reorganization in the early-blind than sighted subjects while the opposite is true for the vision-related occipital network.
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