Palmer describes a "subjective barrier" that limits knowledge of others' experience. We discuss how this barrier extends to all knowledge, becoming less distinct as theoretical constructs are strengthened. We provide evidence for isomorphic experience, among individuals with similar physiologies, by showing that perceived relations between colors are as similar when viewing pigments as when viewing subjective colors caused by flickering bars.

We address two major limitations of Schyns et al. First, we clarify their concept of "features" by postulating several levels for processing. The composition of the feature set at each level determines the set at the next higher level, following simple structural guidelines. Second, we show that our proposed framework reconciles feature-creation and fixed-feature approaches.

People cannot make independent judgements of stimulus attributes and so ''it is necessary to theorize in terms of stimulus structures'' (Lockhead 1992, p. 551) rather than in terms of stimulus features. The new commentaries here further this statement and also support the observations in the target article that psychophysical scaling methods allow us to measure (1) how context determines judgments and (2) what people remember about prior stimuli.

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.

Psychophysical scaling models of the form R = f(I), with R the response and I some intensity of an attribute, all assume that people judge the amounts of an attribute. With simple biases excepted, most also assume that judgments are independent of space, time, and features of the situation other than the one being judged. Many data support these ideas: Magnitude estimations Of brightness (R) increase with luminance (I). Nevertheless, I argue that the general model is wrong. The stabilized retinal image literature shows that nothing is seen if light does not change over time. The classification literature shows that dimensions often combine to produce emergent properties that cannot be described by the elements in the stimulus. These and other effects cannot be adjusted for by simply adding variables to the general model because some factors do not combine linearly. The proposed alternative is that people initially judge the entire stimulus - the object in terms of its environment. This agrees with the constancy literature that shows that objects and their attributes are identified through their relations to other aspects of the scene. That the environment determines judgments is masked in scaling studies where the standard procedure is to hold context constant. In a typical brightness study (where different lights are presented on the same background on different trials) the essential stimulus might be the intensity of the light or a difference between the light and the background. The two are perfectly confounded. This issue is examined in the case of audition. Judgments of the loudness of a tone depend on how much that tone differs from the previous tone in both pitch and loudness. To judge loudness (and other attributes) people first seem to process the stimulus object in terms of differences between it and other aspects in the situation; only then do they assess the feature of interest. Psychophysical judgments will therefore be better interpreted by theories of attention that are based in biology or psychology than those (following Fechner) that are based in classical physics.

Four adult females responded at a computer console, on three constant probability concurrent variable-interval reinforcement schedules. The subjects were instructed to try to obtain as many reinforcers as possible, but were not given any instructions on how to accomplish this task. Three of the four subjects typically allocated responses to the schedule offering the higher reinforcement probability. These results show that some subjects trying to maximize overall reinforcement may respond in accordance with a momentary maximizing strategy.

After using video display terminals (VDT), some persons notice that achromatic patterns appear faintly colored hours after terminal use. We investigated the incidence of this effect, the McCollough effect (ME), among 125 VDT users. Subjects completed a questionnaire regarding work habits and certain life-style aspects. They were shown photographs of varying spatial frequencies to identify the adapting stimulus responsible for the ME. The incidence of ME after routine use of VDTs was 19.1%. The adapting stimulus was the repeating character lines of the VDT. No aspect of life-style investigated appeared to predispose an individual to develop the ME. Those subjects who developed the ME did not differ from those who did not in age, sleep, caffeine consumption, use of medication, refractive errors, or computer usage, nor did they have a higher incidence of ocular defects or eye strain.

Listeners classified three tones that differed in loudness. Two tones were always similar in intensity (2 dB separation). The third tone was either similar to or different from these two tones. Performance depended on this stimulus range: The greater the difference between two tones fixed in intensity and the third tone, the less precise was the discrimination between the two fixed tones. Performance also depended on sequence: Successive responses were positively correlated. The results show that measures of discriminability depend on stimulus range, and that measures of criterion placements change from trial to trial and depend on stimulus sequence.

In two sets of experiments we examined pigeons' discrimination performance with a visual flicker-rate continuum, using a conventional successive discrimination procedure. In the first experiment, responses during the intermediate stimulus value were never reinforced, while responses during stimuli on either end of the continuum were reinforced periodically. In the second experiment, responses during stimuli from one end of the continuum were never reinforced, while responses during stimuli from the other end of the continuum were reinforced periodically. Results from both experiments show that discrimination between unchanged positive and negative stimulus values is a function of the range over which the total stimulus set varies. These range effects are comparable to effects found in absolute judgment tasks in human and animal psychophysics. In addition, the range effects reported here are not due to channel capacity, but may depend instead on variability in judgment criteria.

An illusion reported from classical times is that the horizon moon or sun is much larger than the zenith view of the same object. Explanation has been sought for this illusory magnification of the horizon object by examining the object color, position, and movements of the head or eyes, neural-muscular responses of the observer, sky and ground cues, etc. For the situation reported here, the sun or moon is viewed from an airplane at an altitude of 7 km or more with the head and eyes depressed and is seen as a very small, very red object on an unobstructed horizon. This horizon moon viewed from the air, and the zenith moon viewed from the ground, have in common the absence of a continuously textured field extending from the observer to the horizon, just those cues which prevent empty field myopia. We infer this absence of cues needed to reduce accommodation causes underestimation of the size of distant objects. The analysis, together with a review of the literature, indicates that the classical moon illusion is one of reduction in apparent size of the zenith object rather than overestimation of the size of the horizon object. Indeed, relatively proper judgments about the size of horizon objects are made by observers on the ground who have an unobstructed view to the horizon. The sun and moon really are large, but they appear that way only when viewed in a continuous environment. The moon illusion is considered here to be a part of a more general visual distortion, the toy illusion, in which large, distant objects are judged to be small when they are seen in conditions tending to produce empty field myopia. Thus, the size constancy normally recorded when ground objects are viewed from the ground is lost when these objects are viewed from an airplane at some altitude that separates the viewer from the environment. These ordinary objects are then perceived to be toys rather than full-sized familiar objects.

Two opposing hypotheses are that estimated distances may be used to predict scanning times in mental scanning experiments (Mitchell & Richman, 1980; Pylyshyn, 1981) and that scanning times may be used to estimate distances on maps (Thorndyke, 1981). We tested these hypotheses by having people both estimate lengths and mentally scan diagonal lines, spirals, and mazes. There were large and consistent differences in the rate of scanning the three configurations, regardless of whether people scanned percepts or images. These differences could not be accounted for by differences in length estimates or by people’s tacit knowledge of their scanning rates. We propose that people actually do mental scanning in a mental scanning task rather than use length estimates to generate scanning time and that they do not rely on scanning times to estimate length in a length estimation task.

Subjects judge successive stimuli to be overly similar in psychophysical scaling tasks. This is called assimilation. They also tend to judge each stimulus as overly different from more previous events. This is called contrast. To examine a two-stage linear model of these sequence effects, we asked subjects to judge the relative intensity of successive tones. In support of the model, responses again depended lawfully on prior events. These memory effects occur in a variety of scaling tasks and are consistent with two assumptions: (a)Successive events assimilate in memory, and (b) subjects compare each stimulus to a collection of memories of prior events to generate a response. The trial-by-trial analysis used to test the model also showed that even in magnitude-estimation studies, equal stimulus ratios do not result in equal response ratios, except on average. This article suggests that examinations of trial-by-trial performance might be useful in studying memory and judgment processes.

There are persistent sequential effects in judgment tasks. For example, responses tend to be similar to the value of the just-prior stimulus. This is called assimilation. Also, if feedback is or is not provided after each trial, then responses contrast with or assimilate to, respectively, each of several earlier stimuli in the sequence. These context effects have been shown to be independent of stimulus modality and of the range of stimulus values within a modality. By providing different sets of feedback in order to affect the responses used, this article shows that these sequential effects in judgment data are also independent of the form and range of the scale of responses used to label stimuli.

An abstract is not available for this content so a preview has been provided. Please use the Get access link above for information on how to access this content.