Gregory R. Lockhead

Response system processes in absolute judgment

Consistent relationships are found between Ss′ absolute judgments of the value of a stimulus and the previous sequence of both stimuli and responses. The form and magnitude of these sequential effects are shown to depend on the presence or absence of feedback and on task difficulty. The pattern of the sequential effects found allows the conclusion that they are due to purely response-system processes. A two-stage model of the judgment process is proposed, and it is argued that observed assimilative effects account for the central tendency effects observed in category judgments.

Sequential effects in absolute judgments of loudness

The effects of preceding stimuli on the judgments of current stimuli were examined in a study using absolute judgments of loudness with feedback. It was found that the response on a given trial was dependent on the stimuli in the preceding sequence of at least five trials. Both assimilation and contrast effects were observed. The form of the dependency of a response on a prior stimulus was a function of the ordinal position of the stimulus in the preceding sequence of trials. The stimulus on the immediately preceding trial had an assimilative effect on the response and preceding stimuli two to five trials removed all showed a contrast effect on a given response. The extent to which these preceding stimuli contributed to the contrast effect was an increasing function of their recency. The reversal of the dependency of the response, from assimilation to the stimulus one trial back, to contrast with the stimuli two and more trials back, indicates a unique function of the immediately preceding stimulus in this task. Since there was a reduction in the variance of responses to those stimuli similar in value to the immediately preceding stimulus, it is proposed that the stimulus and feedback on the last trial were remembered and used asa standardin judging the presented stimulus. A model is presented in which it is assumed that the memory of the magnitude of the immediately preceding stimulus is contaminated in specified ways by prior stimuli in the series. The empirical findings of assimilation and contrastare expected consequences of the proposed memorial processes.

Difference information in brightness perception

Contour information generated by moving retinal images has been shown by others to be the principal determinant of perceived color. The data presented here show that, for brightness, this information reflects only differences between adjacent stimulus areas. The entire distribution of difference information from contours in the visual field must be specified in order to predict the brightness at any point.

Psychophysical scaling: Judgments of attributes or objects?

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.

Practically perfect pitch

People who can identify piano notes with essentially no errors (perfect pitch) are much less capable in identifying musical notes produced by sine waves. Thus, frequency is not the only information these people use to identify musical notes; piano notes are complex waveforms or patterns, sine waves are not complex. Musically trained people who do not have perfect pitch ability have considerable difficulty identifying either sine waves or piano notes. As well as this quantitative difference, these two groups of musicians also differ qualitatively. The people in both groups are about equally able to judge octave levels, but people with perfect pitch are excellent in identifying the particular note, e.g., E, independent of its octave, while people without perfect pitch ability are not.

Holistic versus Analytic Process Models: A Reply.

Two classes of stimulus process models are considered in this reply to Dykes and Cooper. It is shown that analytic models which assume that stimuli are initially processed in terms of constituent dimensions do not account for large amounts of published data. It is also shown that the holistic-discriminability model that Dykes and Cooper reject is nonetheless consistent with their results and predicts all of the data for which their analytic model was constructed to account.

Classifying intergral stimuli

Two reported experiments support holistic, as opposed to analytic, processing models for integral stimuli. Speeded classification data from different information-processing tasks (univariate and correlated) were predicted by distance between stimuli in similarity space but not by redundancy. The results of the filtering and condensation tasks and the notion of configural stimuli are also explicable in these terms. It is shown that some operational definitions commonly used to define integral stimuli are usually confounded with stimulus similarity. The assumption of independence between the attributes that combine to form multidimensional stimuli is not always met and is always an empirical question. When these attributes are not independent, physical and psychological spaces are not necessarily the same. Similarity structure is a crucial concern if inferences of cognitive processing are to be based on information-processing task results.

Response scales and sequential effects in judgment

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.

Range and sequence effects in judgment

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.

Saltation through the blind spot

At least three localization illusions can be produced by varying the time relations between two stimuli. Two of these, phi motion and Békésy’s illusion, have been induced in areas lacking receptors. To learn if this also occurred with the third illusion, sensory saltation, people reported their observations when Geldard’s visual rabbit was induced by stimulating points around the optic disk. The rabbit crossed the blind spot as well as other portions of the eyes, and the illusory point was often localized within the region of the blind spot. All three illusions can be localized in an area devoid of receptors.