Distance perception as a function of photographic area of view

Distance perception of depicted objects was examined as a function of photographic area of view. Subjects viewed slides of natural outdoor scenes and directly estimated the distances to specified objects. Area of view was manipulated by means of photographing each scene with lenses of five different focal lengths: 135, 80, 48, 28, and 17 mm. Distance perception along the pictorial depth plane was systematically transformed through changing the photographic area of view: the shorter the focal length of the camera lens, the wider the area of view, and the greater the perceived distance. Linear functions for each subject's distance judgments revealed a very high goodness of fit. Both the y-intercepts and the slopes increased as focal length decreased. The increasing y-intercepts suggest that viewers place themselves farther away from the depicted scene as focal length decreases, compensating for the advancing proximal edge. The increasing slopes suggest that distance information throughout the pictorial depth plane appears to change with focal length. The subjects also made direct judgments of foreground truncation, revealing that foreground truncation decreased as focal length decreased, but that this decrease did not account for the considerable expansion in distance perception.     

NONVOCAL LANGUAGE ACQUISITION IN ADOLESCENTS WITH SEVERE PHYSICAL DISABILITIES: BLISSYMBOL VERSUS ICONIC STIMULUS FORMATS

This study compared training in two language systems for three severely handicapped, nonvocal adolescents: the Bliss symbol system and an iconic picture system. Following baseline, training and review trials were implemented using an alternating treatments design. Daily probes were conducted to assess maintenance, stimulus generalization, and response generalization, and data were collected on spontaneous usage of either language system throughout the school day. Results showed that students required approximately four times as many trials to acquire Bliss symbols as iconic pictures, and that students maintained a higher percentage of iconic pictures. Stimulus generalization occurred in both language systems, while the number of correct responses during responses generalization probes was much greater for the iconic system. Finally, students almost always showed more iconic responses than Bliss responses in daily spontaneous usage. These results suggest that an iconic system might be more readily acquired, maintained, and generalized to daily situations. Implications of these findings for the newly verbal person were discussed.     

Detection of auditory signals occurring at random times: Intensity and duration

Observers attempted to detect a weak auditory signal presented in noise. The onset of the signal was determined by a Poisson process, and only responses occurring 1 sec after signal onset were considered detections. Three latency distributions were measured, the time to a signal onset, the reaction time distribution, and the false-alarm distribution (of responses occurring before a signal onset). A simple two-state model is proposed to account for a discrepancy between the distribution of signal waits and the distribution of false alarms. The hazard functions of the reaction time distributions are considered in detail and a simple accumulation model is proposed to account for the results.     

Two classes of models for magnitude estimation

One class of models assumes that presentation of a signal results in an internal representation as a random variable. Depending on whether the signal is close to or far from the preceding signal, the variance of the representation is smaller or larger. Responses are determined largely by this random variable; however, when the signal is close to the preceding one, the response is generated by modifying the representation multiplicatively by some function of the ratio of the previous response to its representation. Power and linear functions are explored. The form of the random variable is assumed to be that arising from either the timing or the counting model operating on a Poisson process. Detailed analyses are carried out successfully only for the timing model with neural sample sizes independent of intensity; however, the data require the sample to increase with intensity. The linear response function coupled with the constant sample size counting model appears somewhat viable, but detailed calculations are very difficult to carry out. The second class of models postulates a power function relation between magnitude estimates and signals intensity for which the exponent is a Gaussian distributed random variable and the unit is the product of two log normal random variables. Again we assume an attention band such that succesive stimuli that are widely separated in intensity lead to independent samples of the random variables while a variety of assumptions is explored for successive stimuli that are near each other in intensity. Although they each give rise to the qualitative features of the data, estimates of parameters are sufficiently inconsistent that we are led to reject all of the submodels studied.     

Variability and sequential effects in cross-modality matching of area and loudness

Individual subjects' performance was examined for cross-modality matching (CMM) of loudness to visual area, as well as for magnitude estimation (ME) of the component continua. Average exponents of power functions relating response magnitude to stimulus intensity were .73 for area, .20 for loudness, and 2.44 for CMM. Predictions of the CMM exponent based on ME were higher than the empirical values, whereas more accurate predictions were made from magnitude production exponents obtained in a previous study. Sequential dependencies were assessed by comparing the response on trial n to the response on trial n--1. The coefficient of variation of the response ratio Rn/Rn-1 was systematically related to the stimulus ratio Sn/Sn-1 for both area and loudness. The coefficient was lowest for ratios near 1 and increased for larger or smaller values. For CMM, the coefficient of variation appeared to be independent of stimulus ratios. The correlation between log Rn and log Rn-1 was also related to Sn/Sn-1 for both ME and CMM. The correlation was highest when Sn/Sn-1 was 1 and dropped to 0 with increasing stimulus separation, but CMM yielded a shallower function than ME.