GRADER: A computer program that recommends student letter grades

GRADER, a computer program that makes student test and/or course letter grade recommendations to instructors, is described. The program uses an algorithm to combine the content mastery (percentage correct) and peer comparison (“curve”) approaches to set grade cutoffs. In addition to standardizing the procedures with which letter grade cutoffs are made, GRADER may help to reduce instructor grading subjectivity and obviate tendencies toward grade inflation or deflation.     

A simple and sensitive method for monitoring running-wheel movement

A running-wheel movement-detection method is described for use with a modified 1350 Commodore mouse and a Commodore 64, is described. The movement-detection method allows for the detection of partial revolutions and direction of movement, but requires no interface equipment. The modified running wheel is discussed as a new technique that may be useful for bridging empirical and theoretical differences between free-operant and discrete-trial runway procedures.     

The effect of unilateral stellectomy on the regulation of heart rate during behavioral stress

Changes in heart rate were examined during classical aversive conditioning before and after either left (n=10) or right stellectomy (n=8). Heart rate (HR) significantly (p<0.01) increased in response to the conditional stimulus with a further increase noted during the unconditional stimulus. After right stellectomy (RSGx) the aversive stress elicited a significantly (p<0.01) smaller increase in heart rate (peak HR change: control 66.8 +/- 6.0; RSGx 36.1 +/- 6.8 beats/min). In contrast left stellectomy did not significantly alter the heart rate conditional response. Cardioselective beta-adrenergic receptor blockade, metoprolol HCl (BB, 1.0 mg/kg, n=8), significantly (p<0.01) reduced the heart-rate conditional response (peak HR change: control 66.8 +/- 6; BB 25.1 +/- 3.8 beats/min) to the same extent as noted during RSGx. These data suggest that the heart-rate increases elicited by aversive stress are mediated in part by sympathetic nerves that originate or pass through the right stellate ganglion. The residual HR increase noted after RSGx or BB probably results from the withdrawal of cardiac parasympathetic activity.     

Amplitude rise time and the perception of the voiceless affricate/fricative distinction

Variation of amplitude envelope at stimulus onset has been considered to be of primary importance for distinguishing voiceless affricates from fricatives (e.g., |t∫| and |∫|). In earlier perceptual experiments, however, variation in amplitude rise time was confounded with variation in frication duration. In two experiments, these variables were independently manipulated, and their individual and combined effects for perception of |t∫| and |∫| were examined. Variation in amplitude rise time alone was not sufficient to signal the voiceless affricate/fricative contrast in these experiments, but variation in frication duration alone was sufficient.     

Low-dimensional chaos maps learning in a model neuropil (olfactory bulb)

Quantification of a chaotic system can be made by calculating the correlation dimension (D2) of the data that the system generates (Packard et al., 1980). The D2 algorithm, however, requires stationarity of the generator, a feature that biological data rarely reflect (Mayer-Kress et al., 1988). So we developed the “point correlation dimension” (PD2), an algorithm that accurately tracks D2 in linked data of different dimensions (Carpeggiani et al., 1991). We now present a mathematical argument that, for stationary data, individual PD2s converge to D2 and we demonstrate that the algorithm rejects contributions made by bursts of noise. Data were obtained from the surface of the olfactory bulb of the conscious rabbit (64 electrodes, 640 Hz each, 1.3 sec epochs) before and after presentation of a novel or habituated odor. D2 could be calculated in only 1 of 10 novel-odor trials, whereas PD2 could be calculated in all. Both algorithms indicated that a novel odor evokes a spatially uniform dimensional increase. The PD2 uniquely exhibited the dimensional decreases that occur during inspiration and the gradients of mean dimension present during the nonstimulated control state. These control gradients remained unchanged without odor experience, but showed spatially specific PD2 increases following odor habituation. It is interpreted that, 1) the PD2 issensitive, accurate, and appropriate for dimensional assessment of biological data, 2) that during analysis of unfamiliar information a singleglobal process is transiently evoked in the neuropil, and 3) after experience multiplespatially specific processes tonically map the sites of learning. Grant Support: National Institutes of Health, HL 31164 and NS27745     

Orientation-contingent color aftereffects mediated by subjective transparent structures

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n=6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeased more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes, Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Intrusion patterns in rapid serial visual presentation tasks with two response dimensions

A rapid serial visual presentation (RSVP) paradigm using both one and two response dimensions was used to test parallel processing models of stimulus dimensions. Fifty subjects were asked to report the identity and/or color of a target uppercase word inserted in a series of lowercase words. The results produced a predominance of posttarget intrusions for color responses and a predominance of pretarget intrusions for identity responses. The requirement of a response to a second dimension impaired hit rates but did not change the pattern of intrusions. An examination of the distributions of intrusions in each response dimension as a function of the response given to the other dimension showed an unexpectedly high percentage of simultaneous hits, a moderate covariation between both responses, and the same patterns of intrusions when compared with the general distributions. While these results seem to be compatible with parallel models of processing for stimulus dimensions, two modifications to this model are suggested. First, the processing of response dimension(s) needs some attentional resources. Second, provision for a mixed model is indicated, which would include trials where no illusory conjunctions are formed.     

Perceptual restoration of a “missing” speech sound: Auditory induction or illusion?

This study investigated whether the apparent completeness of the acoustic speech signal during phonemic restoration derives from a process of auditory induction (Warren, 1984) or segregation, or whether it is an auditory illusion that accompanies the completion of an abstract phonological representation. Specifically, five experiments tested the prediction of the auditory induction (segregation) hypothesis that active perceptual restoration of an [s] noise that has been replaced with an extraneous noise would use up a portion of that noise’s high-frequency energy and consequently change the perceived pitch (timbre, brightness) of the extraneous noise. Listeners were required to compare the pitch of a target noise, which replaced a fricative noise in a sentence, with that of a probe noise preceding or following the speech. In the first two experiments, a significant tendency was found in favor of the auditory induction hypothesis, although the effect was small and may have been caused by variations in acoustic context. In the following three experiments, a larger variety of stimuli were used and context was controlled more carefully; this yielded negative results. Phoneme identification responses collected in the same experiments, as well as informal observations about the quality of the restored phoneme, suggested that restoration of a fricative phone distinct from the extraneous noise did not occur; rather, the spectrum of the extraneous noise itself influenced phoneme identification. These results suggest that the apparent auditory restoration which accompanies phonemic restoration is illusory, and that the schema-guided process of phoneme restoration does not interact with auditory processing.     

Primacy of dimensions in vibrotactile perception: An evaluation of early holistic models

Early holistic models of perception presume that stimuli composed of interacting dimensions can be experienced initially as undifferentiated. This view, formalized through recourse to a Euclidean geometry of perceptual space, predicts that the orientation of axes used to create stimulus sets is unimportant to performance in speeded classification. We tested this idea by using the interacting vibrotactile dimensions of pitch and loudness. Despite perceivers’ relatively poor experience with these dimensions, we showed that the orientation corresponding to pitch and loudness was unique in vibrotactile perceptual space; subjects classified stimuli more efficiently at this orientation than at other orientations. Certain holistic models also claim that when stimulus differences are small, perceivers can recognize change without distinguishing the kind of change. We tested this idea by using a signal detection analysis of unspeededsame—different decisions. We found that subjects’ ability to notice the kind of change equaled their ability to notice the change alone. In view of these results, which indicate that pitch and loudness are primary in vibrotactile perception, we detail a new conception of dimensional interaction.     

Three-space inference from two-space stimulation

Oblique contours sloping at 30° with respect to the horizontal were presented alone, in combination to form chevrons, or with a vertical line to form arrowhead or Y patterns; they were projected onto a screen in the frontal parallel plane and viewed from positions that gave viewing angles of 90° (normal to the screen’s surface), 53°, or 34°. The perceived orientation of the contours, as assessed by a movable arm that the subjects set to be parallel to the obliques, changed monotonically as a function of viewing angle. The change was as great for single obliques as for combinations of obliques within the chevron, arrowhead, and Y patterns. The results of Experiment 1 were extended in Experiment 2, in which obliques at 30° and 50° with respect to the horizontal were presented singly or in combination as chevron patterns. It is argued that the results of both experiments indicate that single two-space oblique lines are immediately interpreted as lying in three-space and that the changes in perceived orientation are a consequence of this perceptual inference.