Estimation of Mental Effort in Learning Visual Search by Measuring Pupil Response

Perceptual learning refers to the improvement of perceptual sensitivity and performance with training. In this study, we examined whether learning is accompanied by a release from mental effort on the task, leading to automatization of the learned task. For this purpose, we had subjects conduct a visual search for a target, defined by a combination of orientation and spatial frequency, while we monitored their pupil size. It is well known that pupil size reflects the strength of mental effort invested in a task. We found that pupil size increased rapidly as the learning proceeded in the early phase of training and decreased at the later phase to a level half of its maximum value. This result does not support the simple automatization hypothesis. Instead, it suggests that the mental effort and behavioral performance reflect different aspects of perceptual learning. Further, mental effort would be continued to be invested to maintain good performance at a later stage of training

Irinotecan Hydrochloride (CPT-11) in Dialysis Patients with Gastrointestinal Cancer

We investigated changes in drug disposition and toxicities with CPT-11 in 15 dialysis patients with gastrointestinal cancers to clarify whether CPT-11 could be administered safely in such patients. For comparison, the same parameters were also investigated in 10 cancer patients not undergoing dialysis. Items investigated included (1) plasma concentrations of SN-38, SN-38G and CPT-11 at 0, 1, 12, 24, 36, 48 and 72h after administration, together with a comparison of mean AUC values for 3 dose levels of CPT-11 (50, 60 and 70mg/m2) in dialysis patients and controls;and (2) occurrence of adverse events. Several findings emerged from this study:(1) No significant difference was observed in the AUC for SN-38 or CPT-11 between the dialysis and control groups;(2) The AUC for SN-38G at each dose was significantly higher in dialysis patients;and (3) Grade 1-4 leucopenia was observed in 11 of the dialysis patients. One patient developed grade 4 leucopenia and died due to sepsis. Anorexia, diarrhea, nausea, alopecia and interstitial pneumonia occurred in 6 dialysis patients. We found changes in drug dispositions of CPT-11, SN-38 and SN-38G in dialysis patients, suggesting that hepatic excretion, especially that of SN-38G, was increased. No significant difference in occurrence of adverse events was observed between the 2 groups. This indicates that CPT-11 can be administered safely in patients on dialysis.</p

P3-17: Why is it Difficult to See Moving Objects in the Dusk? Visual Motion Priming Reveals Two Motion Mechanisms Functioning under Mesopic Vision

We know empirically that perception of moving objects deteriorates in the dusk. The purpose of this study is to reveal the reason of such sensitivity degradation under mesopic vision, when both cones and rods operate. For the purpose, we utilized a phenomenon called visual motion priming, in which the perceived direction of a directionally ambiguous test stimulus is influenced by the moving direction of a preceding priming stimulus. Participants judged the perceived direction of 180 deg phase-shifted, thus directionally ambiguous, sine-wave grating (test stimulus) followed by a smoothly drifting priming stimulus under three different retinal illuminance levels: photopic, mesopic, and scotopic levels, respectively. The spatial distance between priming and test stimuli was varied from 0 deg to 10 deg in visual angle. When the stimuli were high-contrast, the test stimulus was perceived to move in the same direction as the primer (positive priming) under photopic level, while the test stimulus was perceived to move in the opposite direction of the primer (negative priming) under scotopic level. Neither positive nor negative priming was observed under mesopic level. When the stimuli were low-contrast and spatially separated, however, only negative priming was observed regardless of the retinal illuminance level. These results suggest that a higher-order motion system such as a feature-tracking mechanism is functioning to induce visual motion perception under photopic level, while a first-order center-surround motion system is functioning under scotopic level. We speculate that the concurrent activation of different motion mechanisms induces a degradation of motion sensitivity under mesopic vision

Modulation of perceived contrast by a moving surround

The apparent contrast of a center pattern depends on the contrast of its surround. To examine the suprathreshold perception of moving patterns, we measured the perceived contrast of a moving grating while the direction and speed of the surround patterns varied. Subjects matched the apparent contrast of a center patch embedded in surround patches to that of a patch with no surround pattern. Temporal frequency, Michelson contrast and movement direction of both center and surround patterns varied systematically. We found that: (1) contrast reduction is most prominent when the center and surround have the same velocity (velocity selectivity); (2) contrast enhancement occurs when the surround moves at a higher speed than the center, if the difference in temporal frequencies of center and surround exceeds 10–20, independent of the directional relationship between center and surround; (3) contrast reduction is stronger for higher surround contrasts with lower center contrasts; and (4) contrast enhancement is relatively unaffected by center and surround contrasts. We conclude that the contrast perception of moving patterns is influenced by directionally-selective mechanisms except at high temporal frequencies. Our results further suggest tha

In the Dark: Seeing Bikes at Night

Photo of the Olympic Rings lit on a hill overlooking Salt Lake City during the 2002 Winter Olympic