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Biomedical subjects

J C Baird

Publications and source records attributed to J C Baird.

At least 19 recordsLinked to original sources
PubMed1996

Magnitude estimation of perceived odor intensity: empirical and theoretical properties.

Four subjects judged the odor intensities of 7 pyridine concentrations and a blank. Computer simulations of a judgment model were compared with the empirical data. The model generates data patterns that closely mimic empirical findings. The following patterns were confirmed: (a) A power function relates magnitude estimates and concentration with an exponent in the range of 0.7 to 1.0 (b) The exponent fluctuates so that the level constant is negatively correlated with the exponent. (c) The standard deviation of the responses is a negatively accelerated function of the mean. (d) The skewness of the responses is relatively high for low concentrations and declines toward zero with increasing concentration. (e) The correlation between responses to successive stimuli is highest when successive concentrations are similar.

Adult↗
PubMed1995

On the nature and meaning of sinuosity in magnitude-estimation functions.

Magnitude-estimation functions for single observers, derived from multiple judgments of closely spaced stimuli, exhibit a sinuous form in logarithmic coordinates, an observation frequently confirmed since first reported by Luce and Mo (1965). We propose that this can result from reliance on a restricted pool of responses, called "preferred numbers" by Baird and Noma (1975). We describe a model featuring a response band centered on an assumed power function, from which the observer selects from among preferred numbers with equal probability. In simulations, the expected values of these selections oscillate around the underlying power function with an appearance similar to that of Luce-Mo functions. The appearance of these functions depends on values assumed for the scale factor of the power function, the range of intensities considered, and the width of the band from which responses are drawn. We conclude that sinuosity in magnitude-estimation functions does not disconfirm the psychophysical power law.

Arousal↗
PubMed1995

Binaural summation after learning psychophysical functions for loudness.

Do response-related processes affect perceptual processes? Sometimes they may: Algom and Marks (1990) produced different loudness exponents by manipulating stimulus range, and thereby also modified the rules of loudness summation determined by magnitude scaling. The present study manipulated exponents by having a dozen subjects learn prescribed power functions with exponents of 0.3, 0.6, or 1.2 (re sound pressure). Subjects gave magnitude estimates of the loudness of binaural signals during training, and of monaural and binaural signals after training. During training, subjects' responses followed the nominal functions reasonably well. Immediately following training, subjects applied the numeric response scales uniformly to binaural and monaural signals alike; the implicit monaural-binaural loudness matches, and thus the basic rules underlying binaural summation, were unaffected by the exponent learned. Comparison of these results with those of Algom and Marks leads us to conclude that changing stimulus range likely influences underlying perceptual events, whereas "calibrating" a loudness scale through pretraining leaves the perceptual processes unaffected.

Adult↗
PubMed1993

The effects of size, clutter, and complexity on vanishing-point distances in visual imagery.

The portrayal of vanishing-point distances in visual imagery was examined in six experiments. In all experiments, subjects formed visual images of squares, and the squares were to be oriented orthogonally to subjects' line of sight. The squares differed in their level of surface complexity, and were either undivided, divided into 4 equally sized smaller squares, or divided into 16 equally sized smaller squares. Squares also differed in stated referent size, and ranged from 3 in. to 128 ft along each side. After subjects had formed an image of a specified square, they transformed their image so that the square was portrayed to move away from them. Eventually, the imaged square was portrayed to be so far away that if it were any further away, it could not be identified. Subjects estimated the distance to the square that was portrayed in their image at that time, the vanishing-point distance, and the relationship between stated referent size and imaged vanishing-point distance was best described by a power function with an exponent less than 1. In general, there were trends for exponents (slopes on log axes) to increase slightly and for multiplicative constants (y intercepts on log axes) to decrease as surface complexity increased. No differences in exponents or in multiplicative constants were found when the vanishing-point was approached from either subthreshold or suprathreshold directions. When clutter in the form of additional imaged objects located to either side of the primary imaged object was added to the image, the exponent of the vanishing-point function increased slightly and the multiplicative constant decreased. The success of a power function (and the failure of the size-distance invariance hypothesis) in describing the vanishing-point distance function calls into question the notions (a) that a constant grain size exists in the imaginal visual field at a given location and (b) that grain size specifies a lower limit in the storage of information in visual images.

Adult↗
PubMed1991

Transformation theory of size judgment.

Perception of size is assessed by having observers adjust a comparison target at a fixed distance to match the size of a standard located at different distances. Results depend on instructions, target orientation, and available stimulus cues. A mathematical theory assumes that the brain performs an inverse transformation on the proximal information impinging on the retina to recover the original distal size of the target. Results depend on the target visual angle, and the effective target distance and orientation applied in performing the inverse transformation. Effective values are linked to instructions, target location, and stimulus cues. Two models are developed and successfully fit to empirical data. One emphasizes the distance parameter; the second, the orientation parameter.

Attention↗
PubMed1991

Stimulus sequence and the exponent of the power function for loudness.

In two experiments, 15 and 13 subjects estimated the loudness of 12 sound-pressure levels (38-104 dB; 6-dB intervals) of a 1000-Hz tone by the method of magnitude estimation with a modulus assigned to the first stimulus presented. The tone duration was 1 sec. and the interstimulus interval was 6 sec. The presentation order was systematically ascending-descending in one experiment and balanced-irregular in the other. The results indicate that (1) loudness is a power function of sound pressure with an exponent of 0.60 for the systematic order and 0.29 for the irregular order. (2) For both the irregular and systematic orders, a large step-size (12 or 18 dB) between the stimulus on Trial n and on Trial n-1 (or n-3) results in a slight assimilation effect. This also occurs for the small step-size (6 dB) in the irregular order. (3) The size of momentary exponents (based on two points, Trials n and n-1 or n-3) depends on the sound pressures of successive stimuli, whether the steps are positive or negative, and whether the stimuli have been presented in systematic or irregular order. For positive steps, the momentary exponent is lower for a soft tone (Trial n) than for a loud tone, whereas for negative steps the momentary exponent is lower for a loud tone than for a soft tone. These effects ar more pronounced when these stimuli are presented in an irregular order. A relative judgment model is offered for magnitude estimation. It assumes that subjects judge the loudness of a stimulus in terms of three reference markers: the minimum and maximum sound pressures as well as the sound pressure of the previous stimulus.

Adult↗
PubMed1990

A simple but powerful theory of the moon illusion.

Modification of Restle's theory (1970) explains the moon illusion and related phenomena on the basis of three principles: (1) The apparent sizes of objects are their perceived visual angles. (2) The apparent size of the moon is determined by the ratio of the angular extent of the moon relative to the extents subtended by objects composing the surrounding context, such as the sky and things on the ground. (3) The visual extents subtended by common objects of a constant physical size decrease systematically with increasing distance from the observer. Further development of this theory requires specification of both the components of the surrounding context and their relative importance in determining the apparent size and distance of the moon.

Distance Perception↗
PubMed1989

Imagery, memory, and size-distance invariance.

The size-distance invariance hypothesis (SDIH) was examined for remembered and imaged stimuli. In Experiment 1, subjects gave remembered and imaged distances of familiar objects and imaged distance of nondescript rods. The relationship between stated size and distance is more adequately described by power functions with exponents less than 1 than by the more restricted SDIH (exponent of 1). In Experiment 2, subjects gave distance estimates to recalled and imaged familiar objects and described the visual context in which each object was situated. A different group then sorted the contexts into categories based on general similarity. There were no significant differences between distance estimates based on memory and those based on imagery, and the visual contexts were not sorted according to whether they were generated in the memory or in the imagery conditions. In Experiment 3, subjects estimated the distances to objects in an outdoor setting. A linear relationship was found between estimated and physical distance, suggesting that the lower exponents obtained in Experiments 1 and 2 were not artifacts of the distance judgment procedure.

Adult↗
PubMed1989

Shift in stimulus range and the exponent of the power function for loudness.

The exponent of the power function for loudness was tracked over the course of 60 trials with one stimulus range and compared to the exponent over the course of 60 subsequent trials with a different stimulus range. Three stimulus sets were used: (1) weak, a short range of relatively soft tones (45-55 dBA); (2) strong, a short range of relatively loud tones (64-74 dBA); and (3) complete, a longer range of soft to loud tones (40-90 dBA). All pairs of stimulus sets were tested, together with three control conditions in which no shift in range occurred. Ten subjects were run in each of the nine groups. For preshift trials, the mean exponent was lowest for the strong stimulus series, highest for the weak series, and at an intermediate value for the complete series. These differences were all significant. Following a shift in stimulus range, the weak series still yielded the highest exponent, but the exponents were not reliably different for the complete and strong series. Postshift exponents also depended significantly on the preshift range experienced by the subjects. These effects were not confined to the period immediately following the shift in range, but persisted for up to 60 trials.

Attention↗
PubMed1988

Overflow, first-sight, and vanishing point distances in visual imagery.

The relationship between the size of a familiar object and the distances at which it is imaged is examined in three experiments. The distance at which an imaged object overflows the visual field is linearly related to object size, a result consistent with the size-distance invariance hypothesis (Kosslyn, 1980). The distance at which an object is initially imaged, first-sight distance, is related to the object size by a power function with an exponent less than 1. In addition, time required to scan from the first-sight to the overflow distance increases as a function of the difference between the two distance estimates. The distance at which an imaged object becomes too small to be identified, vanishing point distance, is related to object size by a power function with an exponent less than 1. This result does not support predictions made from the size-distance invariance hypothesis or Kosslyn's model of visual imagery. Implications for a theory of visual imagery and memory are discussed.

Adult↗
PubMed1982

The moon illusion: I. How high is the sky?

The most common explanations of the moon illusion assume that the moon is seen at a specific distance in the sky, which is perceived as a definite surface. A decrease in the apparent distance to the sky with increasing elevation presumably leads to a corresponding decrease in apparent size. In Experiment 1 observers (N = 24) gave magnitude estimates of the distance to the night sky at different elevations. The results did not support the flattened-dome hypothesis. In Experiment 2 observers (N = 20) gave magnitude estimates of the distance to the sky at points around a 360 degrees circle just above the horizon. The results were consistent with those of Experiment 1, and in addition, estimates were highly correlated with the physical distances of buildings at the horizon. In a third, control experiment, observers (N = 20) gave magnitude estimates of the distances of buildings at the horizon. A power function fit the relation between estimated and physical distance (exponent = 1.17) as well as the relation between estimates of the sky points above the buildings (Experiment 2) and estimates of building distances (exponent = .46). Taken together, the results disconfirm all theories that attribute the moon illusion to a "sky illusion" of the sort exemplified by the flattened-dome hypothesis.

Astronomical Phenomena↗
PubMed1982

The moon illusion: II. A reference theory.

The present theory provides explanations for the moon illusion and related issues involving size and distance perception in natural, outdoor settings. Although some assumptions of previous theories are rejected, other pivotal aspects are retained in this formulation. In particular, the present theory states that both the sky and ground are important referents in judging the spatial extent of the moon. Neither factor alone can account for all the available data, but quantitative models incorporating both factors do quite well when applied to the parametric findings of Holway and Boring, as well as to the results obtained by Kaufman and Rock. The reference theory and its associated class of specific models suggest new theoretical directions and experimental tests to narrow yet further the selection of appropriate explanations for one of visual perception's oldest unsolved puzzles.

Astronomical Phenomena↗
PubMed1980

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.

Adult↗