Ratio responding as a function of concurrent avoidance schedules, yoked shocks, and ratio value.

Fixed-ratio food-reinforced responding in rats was studied alone and with concurrent shock avoidance or with concurrent response-independent shocks matched to those that occurred in the avoidance condition. Under each condition, fixed-ratio size was increased over successive daily sessions. Fixed-ratio response rate generally passed through a maximum as a function of fixed-ratio size. Decreased fixed-ratio responding at values beyond the maximum occurred when (1) the time to complete a fixed ratio approximated the response-shock interval of the avoidance schedule, (2) the shock rate increased, and/or (3) the ratio requirements were so high that ratio strain occurred. Avoidance rates decreased slightly as fixed-ratio size increased.

Improved detection of human breast lesions following experimental training.

This study was designed to evaluate the effect of breast examination training with silicone models on the detection of lesions in natural breast tissue. Six women with a total of 13 benign breast lumps were examined by 20 trainees before and after a 20--30 minute training session or a period of unrelated activity. Following the training, percentage of correct detections, duration of examination, and reports of false positives increased. Confidence in correct detections and false positives also increased, although confidence in correct detections was greater than confidence in false positives. The results indicate the effectiveness of the training and suggest a need for a more complex model for training discrimination between normal nodularity and breast lesions.

Static and kinetic properties of the dolphin pupil.

In dim illumination, adult human pupil area becomes asymptotic at about 51 mm2 whereas the dolphin pupil achieves an area of about 70 mm2 under equivalent conditions. At moderate illumination levels (greater than 100 lx), the dolphin pupil becomes a horizontally oriented ellipse and develops a pronounced central constriction with additional light. The relative relationship between pupil area and illumination copmares closely with published human data. Rates of pupil response to step increments in illumination are very similar for the two species. Although the pupil has been proposed as a mechanism for correction of the dolphins' high aerial myopia, correlation of the laboratory findings on static and kinetic pupil properties with visually controlled aerial behaviors disclosed no special interdependence.

Effects of certain training parameters on detection of simulated breast cancer.

Forty-two female subjects, constituting 14 groups, palpated a silicone breast model in a lump detection task. Three variables, number of trials (amount of practice), search pattern requirement (restricted vs. unrestricted), and the presence or absence of lumps, were manipulated according to 3 x 2 x 2 design. The effect of all modes of practice on detection performance in posttest 1 was evidenced by an increase in percent of lumps detected and a decrease in detection threshold, but no form of practice was superior to the others. Following posttest 1 a brief search-training procedure was administered to 39 subjects which further lowered detection threshold, increased percent of lumps detected, and increased trial duration in posttest 2. The results indicate the effectiveness of the training procedure for improving detection ability and suggest the need for a more complex model to determine more specifically the effects of the practice models employed.

Optokinetic suppression of aberrant vestibular reactions: an observation.

It has long been known that optokinetic nystagmus may be modified by vestibular inputs. We have suppressed an aberrant vestibular response and associated gastrointestinal sensations by use of an optokinetic stimulus simultaneous to the positional stimulus in a patient with paroxysmal positional vertigo. This single subject study utilized several optokinetic conditions, and patterned its stimulus presentations to control for visual fixation and vestibular habituation. Objective recordings of eye movements (ENG) were made simultaneously with subjective evaluation of "dizziness" on a simple magnitude estimation scale.

Improved treatment via home monitoring refractory vertigo.

The ubiquity of dizziness in clinical practice and the complexity of diagnosis and treatment has necessitated the development of a home monitoring procedure which assists the patient in collecting information concerning the course of his condition and his condition and his response to therapy. A case report of a patient with refractory, long-term, posttraumatic vertigo is presented to demonstrate the feasibility and utility of this procedure. It was found that (1) the patient was able to monitor his progress continuously for 118 days; (2) the information generated appeared to be valid; and (3) this information was integrally associated with a functional improvement in the patient's condition.

Slow axonal protein transport and visual function following retinal and optic nerve ischemia.

Retinal ganglion cell protein synthesis and slow axonal protein flow have been measured in eight optic nerves from four macacus rhesus monkeys after producing ganglion cell ischemia. Comparison of the slow axonal protein flowing into the two optic nerves of the same control animal reveals a variability of up to 27 per cent. Following central retinal artery ligation, infarction of the retinal ganglion cells was reflected by a 97 per cent reduction in the radioactively labeled protein within the optic nerve. This profound reduction in labeled protein within the nerve confirmed that only ganglion cell dependent intra-axonal protein flow was being measured. Ischemia to the ganglion cell axons, with preservation of blood flow to the cell soma, was obtained in two optic nerves from different animals by severing all the posterior ciliary vessels entering about the optic nerve. Six weeks later, only a modest histologic loss of axons was present in these optic nerves. However, a profound reduction (up to 97 per cent) in labeled optic nerve protein was found at four days following intravitreal leucine injection. This is the time when the optic nerve slow axonal protein flow is dominated by the foveomacular ganglion cells. The reduction in slow axonal protein flow corresponds histologically to a preferential retrograde degeneration of the foveomacular ganglion cells, suggesting increased sensitivity of the smaller foveal axons to the induced ischemia. Electrophysiologic measurements support this conduction.