Further tests of an exemplar-similarity approach to relating identification and categorization

Further tests were provided of an exemplar-similarity model for relating the identification and categorization of separable-dimension stimuli (Nosofsky, 1986). On the basis of confusion errors in an identification paradigm, a multidimensional scaling (MDS) solution was derived for a set of 16 separable-dimension stimuli. This MDS solution was then used in conjunction with the exemplar-similarity model to accurately predict performance in four separate categorization paradigms with the same stimuli. A key to achieving the accurate quantitative fits was the assumption that a selective attention process systematically modifies similarities among exemplars across different category structures. The tests reported go well beyond earlier ones (Nosofsky, 1986) in demonstrating the generalizability and utility of the theoretical approach. Implications of the results for alternative quantitative models of classification performance, including Ashby and Perrin's (1988) general recognition theory, were also considered.     

Search performance without eye movements

Visual search performance (with sets chosen to elicit both serial and parallel search patterns) under two conditions that precluded saccades was compared to the typical situation in which visual inspection of the array is possible. In one condition, the display duration was so brief that any saccades that were executed would be too late to bring the targeted portion of the array into the fovea. In the other, the display remained present until the subject's response, but eye position was monitored and trials with shifts in fixation were excluded from analysis. The latter condition produced search latencies that were nearly identical to those with free inspection. Brief exposure, in contrast, did not produce the pattern typical of serial search, presumably because of strategies induced to deal with the rapid decay of the visual array. It is concluded that saccadic eye movements play little role in the patterns of performance used to infer serial and parallel search, and that brief exposure is not a satisfactory technique for exploring the role of saccadic eye movements in visual search.     

Measurements of gaze movements while driving

In this study, gaze movements of drivers driving through an intersection were investigated. Gaze movements of drivers in large vehicles were compared with those in small vehicles. There were both similarities and differences in the visual search behaviors of drivers of large and small vehicles. The two groups were similar in that, when approaching an intersection, drivers made repeated saccadic gaze movements; after entering the intersection, saccadic gaze movements were directed ahead in the direction of turning. Differences arose in the frequency and distribution of gaze movements. The number of gaze movements was significantly greater in drivers of large vehicles. The distribution of gaze movements in driving a large vehicle showed a peak at the point 50 to 60 degrees to the right and left of the median plane of the driver. The distribution of gaze movements of drivers of small vehicles showed no peak across the visual field.     

Mood profiles of Masters track and field athletes

In several studies attributing positive health benefits to running, the benefits include reduced depression, fatigue, anger, and increased vigor. Until now, little research has focused on Masters track and field athletes. The present study reports on 587 men and women Masters who participated in a mailed survey measuring mood states using the Profile of Mood States. In comparison to other groups of athletes, these Masters tend to be less depressed, less angry, and less fatigued. Attribution to lifestyle and maturity with their sport is discussed.     

Changes in the incidence of nocturnal bruxism in college students: 1966-1989

The frequency of self-reported nocturnal bruxism in three large samples of college undergraduates was compared as a means of assessing change in the incidence of this disorder since 1966. We found the incidence of nocturnal bruxism had increased from 5.1% to 20.5% in college students over the period covered by these studies.     

H-reflexes during a motor skill acquisition task

H-reflex amplitudes were studied during the acquisition of a motor skill involving coordinated isometric plantarflexion at the ankle joints as subjects learned to trace a triangular pattern on an oscilloscope screen by controlling plantarflexion torque applied against load cells. Torque feedback was presented on a subject oscilloscope with the right foot controlling a vertical cursor and the left foot a horizontal cursor. Eleven subjects reached criterion performance. H-reflexes were recorded from the right soleus and timed to the initiation of soleus muscle activity to plantarflex the foot. Average time to complete one trial decreased from 9 sec. in the prelearning block to 4 sec. postlearning. No single learning strategy was evident as subjects varied widely in their levels of H-reflex amplitude, but during postlearning, H-reflex amplitude became consistent within subjects as tracing performance became faster and accurate.     

Do response time advantage and interference reflect the order of processing of global- and local-level information?

Navon's (1977) global precedence hypothesis was based primarily on the joint occurrence of two effects: a response time (RT) advantage for identifying global targets, and interference by global distractors on responding to local targets. Although the hypothesis has been questioned on the basis of experiments in which it has been shown that a local RT advantage and local interference can occur, it is still frequently assumed that these two effects are a valid measure of the order in which local and global levels of structure are processed. In the present experiment, this assumption was examined. Subjects identified target letters that occurred randomly at the global or local level in a divided-attention task. The visual angle subtended by the stimulus pattern was varied, a manipulation known to affect the relative speed of response to local- or global-level information. Local targets were identified faster than global targets at the larger visual angles, but there was no difference in RT at the smallest visual angle. Despite this change in RT advantage, the interference effect did not change as a function of the visual angle of the stimulus pattern. Moreover, global distractors interfered with responding to local targets but local targets had no effect on responding to global targets, which is exactly the opposite of the finding one would expect if RT advantage and interference reflected order of processing. These findings are not consistent with the assumption that RT advantage and interference reflect order of processing in a simple way.     

Instructional and probability manipulations of bias in multiletter matching

Ratcliff (1985) performed fits of his diffusion model to the results of multiletter-matching experiments conducted by Ratcliff and Hacker (1981) and Proctor, Rao, and Hurst (1984), in which bias to respond "same" or "different" was manipulated by instructions and probabilities, respectively. The fits showed that both bias manipulations affected settings of a goodness-of-match criterion, whereas instructions also affected sensitivity. Evaluations of the experimental procedures and of Ratcliff's model-fitting procedures were performed in the present study. Three experiments showed that instructions and probabilities had similar effects, regardless of whether the different pairs were blocked or randomized according to the number of mismatching positions. The most salient feature of the results--that "same" reaction times were traded off more than were "different" reaction times, with no corresponding asymmetry in the error rates--was evident in all situations. The evaluation of Ratcliff's model-fitting procedures indicated that the apparent influence of instructions on sensitivity likely is an artifact of unequal variance for the sets of same and different pairs. Moreover, the effects of bias can be explained in terms of settings of response criteria, rather than of the goodness-of-match criterion, as in Ratcliff's fits.     

Human optokinetic nystagmus: competition between stationary and moving displays

We reported earlier that occlusion of the central retina and stationary edges have highly interactive effects on the gain of optokinetic nystagmus (OKN; Murasugi, Howard, & Ohmi, 1986). In this study, we explored this effect in more detail. A central occluding band of variable height, flanked by vertical bars, was superimposed onto an array of dots moving at 30 degrees per second. The height of the occluding band required to abolish OKN increased with the separation of the vertical bars. For bars 3.5 degrees apart, OKN was abolished in most subjects when a band only 6' high ran between them. For bars 75 degrees apart, a band at least 20 degrees in height was required to abolish the response. The effects of the stationary figure depended to some extent on the subject's attention, but only at intermediate values of bar separation. Both low- and high-level mechanisms are proposed to account for the results.     

Texture perception in sighted and blind observers

The purpose of the present study was to evaluate the utility of visual imagery for texture perception. In Experiment 1, sighted, early-blind, and late-blind observers made relative smoothness judgments of abrasive surfaces using active or passive tough. In Experiment 2, subjects compared vision and touch in the accuracy of smoothness detection, using a broad range of textures, including very fine surfaces. No differences appeared between the sighted and the blind, and it did not matter if touch were active or passive. Vision and touch showed similar performance with relatively coarse textures, but touch was superior to vision for much finer surface textures. The results were consistent with the notion that visual coding of tactual stimuli is not advantageous (or necessary) for texture perception, since touch may hold advantages for the detection of the smoothness of surfaces.