Cue discrimination and forgetting

Subjects learned paired associate fists in which word triads were paired with nouns to a partial criterion; they were then given both an immediate and a 1-week delayed recognition test for discrimination among the triads and a cued recall test. Recall after 1 week was slightly poorer than that occurring immediately, but it was unaffected by various patterns of element identity among the triads. Discrimination improved somewhat over the 1-week interval. Further experiments showed that the immediate test was responsible for both reducing forgetting and improving discrimination, but both effects were independent of identity structure. Forgetting cannot be attributed to loss of differentiation of cues.     

Entropy and variability discrimination

Two experiments examined college students' discrimination of complex visual displays that involved different degrees of variability or "entropy." Displays depicted 16 black and white line drawings of various types (e.g., a brain, a clock, a hand); the participants were required to classify a display in terms of its variability (e.g., a low-variability display contains many identical items, whereas a high-variability display contains few identical items). The participants' accuracy and reaction time scores on a 2-alternative forced-choice discrimination disclosed that people can and do use entropy to classify different levels of visual display variability. Individuals differed in their use of absolute rather than relative entropy.     

Metacontrast and brightness discrimination

An attempt was made to obtain U-shaped masking functions in two metacontrast experiments. Trained Ss judged whether a square test stimulus (TS) was bright or dim. The TS was presented alone or in conjunction with an adjacent pair of square masking stimuli (MS) whose energy equaled the bright TS. The stimulus onset asynchronies (SOA) rangedfrom 0 to 125 msec. The task minimized the role of apparent movement cues as a reliable basis for judgrnent. Similar studies have employed TS plus MS vs MS alone as the alternatives, allowing apparent movement to be a cue. Brightness accuracy was a U-shaped function of SOA. This finding is consistent with neural-net models (Weisstein, 1968). However, analysis of Ss’ response bias suggested an alternative explanation involving the MS as a comparison stimulus at short SOA. It was concluded that U-shaped masking functions are also consistent with theories based upon independent component processes, e.g., Schurman and Eriksen (1970) and Uttal (1970).     

Loudness and loudness discrimination

A model is developed which holds that pure-tone intensity discrimination and suprathreshold loudness judgments are based on the same sensory representation. In this model, loudness is a power function of sound intensity. When two tones are presented sequentially, each gives rise to a loudness value along the sensory continuum. In intensity-discrimination experiments, threshold is reached when the loudness difference between the tones exceeds a criterial value. For suprathreshold presentations of tone pairs, judgments of loudness differences are based on the loudness difference between the two tones. The model is shown to accord well with data from both classes of experiments.     

Impartiality and disability discrimination

Cost-effectiveness analysis is the standard analytical tool for evaluating the aggregate health benefits of treatments and health programs. According to a common objection, however, its use may lead to unfair discrimination against people with disabilities. Since the disability discrimination objection is seldom articulated in a precise way, I first provide a formulation that avoids some implausible implications. Then I turn to the standard defense of cost-effectiveness analysis and argue that it does not succeed. But this does not settle the question of whether the use of cost-effectiveness analysis leads to unfair discrimination. Rather, it shows that the controversy should be approached in a different way. Thus, I conclude by outlining an alternative strategy for answering the question.     

Color discrimination and luminance

This experiment studied the relation between luminance level and color discrimination at 570 millimicrons. A variety ofstimuli whose luminances varied from .1 to 100 ft-L were viewed against a variety of surrounds. 1t was found that color discrimination ability was a joint function of the luminance level of the stimulus and the ratio of the luminance of the stimulus to that of the surround.     

Counterfactual discrimination

In counterfactual cases of discrimination, an agent would have treated someone worse had circumstances been different such that instead of being a member of her actual group, she was a member of some other group. The case for considering such cases to be genuine cases of discrimination is bolstered by the fact that we are inclined to say that cases where an agent would have treated someone better had she been a member of another group are discriminatory. But I argue that the cases are relevantly different: in one kind of case, but not the other, a person is harmed. I then consider and reject a number of objections to this suggestion.     

Memory retrieval and discrimination learning

A better reinforcement schedule may be associated with one exteroceptive stimulus (S+) than with another exteroceptive stimulus (S−). While all theories agree that performance in such discrimination tasks is affected by the reinforcement schedules associated with the exteroceptive S+ and S− cues, some theories suggest that performance is also affected by the reinforcement schedule associated with interoceptive reward produced cues. The two experiments reported here were concerned with identifying the conditions under which the interoceptive cues produced by nonreward come to affect performance. According to one hypothesis, such cues will acquire control over approach responding if animals make an approach response in their presence, but not otherwise. According to the memory hypothesis, the memory of nonreinforcement will become a signal for reinforcement, thus invigorating performance, if it is retrieved on a rewarded trial. In two experiments, two groups made strong approach responses to the nonreinforced cues on S− trials, but the memory of nonreward was better retrieved on a subsequent rewarded trial in one group than in the other. Subsequently, both groups were extinguished. The extinction findings support the memory view.     

Transference,discrimination and reversal

A total of 68 subjects-17 normal volunteers, 17 hospitalized paranoid schizophrenics, 17 non-paranoid schizophrenics, and 17 patients with organic brain syndrome-were compared on their performance on the different phases of a specially devised conditioning procedure. This procedure is composed of (1) acquistion of the conditional reflex,i.e., squeezing a rubber bulb to the presentation of white light; (2) transference from a visual conditional stimulus to a verbal conditional stimulus and back to the visual conditional stimulus; (3) conditional stimulus differentiation; and (4) conditional stimulus reversal. Performance profiles of the normal and of the pathological groups were established and the statistically significant differences among the sub-groups of the experimental population were described. The clinical significance of these findings is discussed.     

Conditioned reinforcement and discrimination performance

Pigeons were trained in a three-key chamber to peck one side key in the presence of a vertical line on the center key and to peck the other side key in the presence of a horizontal line. Correct choice responses were reinforced with food according to fixed- and variable-ratio, fixed-interval, and differential-reinforcement-of-long-latency schedules of reinforcement. For each schedule, the birds performed under each of two conditions: (1) each correct choice response produced a brief presentation of stimuli intermittently paired with food, then the next trial; (2) each correct choice response produced an intertrial interval only. For all schedules except one long latency schedule, response rates were higher under the condition of brief stimulus presentation than under the comparable control condition. Presentation of brief magazine stimuli increased choice accuracy. The amount of change in accuracy was correlated with the rate of food presentation. Performance under the schedules with highest food reinforcement rates showed no enhancement; performance under the schedules with the lowest reinforcement rates showed the greatest enhancement.     

Dichoptic and dichotic micropattern discrimination

Ss compared two rapidly successive, brief, discriminably different stimulus elements, called a micropattern, with a second micropattern composed of the same two stimulus elements presented in reverse temporal order. Discriminations could be made between two such micropatterns in the monaural (monocular) as well as in the dichotic (dichoptic) modes of presentation. Discrimination between micropatterns was based on the perceptual dominance of the temporally trailing stimulus element in both modalities and in both modes of presentation. While monaural (monocular) micropattern discrimination is significantly superior to dichotic (dichoptic) discrimination, the existence of dichotic (dichoptic) discrimination demonstrates that no essential peripheral process is required for micropattern discrimination.     

Variable foreperiods and temporal discrimination

Temporal judgements are often accounted for by a single-clock hypothesis. The output of such a clock is reported to depend on the allocation of attention. In the present series of experiments, the influence of attention on temporal information processing is investigated by systematic variations of the period preceding brief empty intervals to be judged. Two indicators of timing performance, temporal sensitivity, reflecting discrimination performance, and perceived duration served as dependent variables. Foreperiods ranged from 0.3 to 0.6 s in Experiments 1 to 4. When the foreperiod varied randomly from trial to trial, perceived duration was longer with increasing length of foreperiod (Experiments 1 and 3 with brief auditory markers and Experiment 4 with brief visual markers), an effect that disappeared with no trial-to-trial variations (Experiment 2). Longer foreperiods also enhanced performance on temporal discrimination of auditory empty intervals with a base duration of 100 ms (Experiments 1 and 5), whereas discrimination performance was unaffected for auditory intervals with a base duration of 500 ms (Experiment 3). The variable-foreperiod effect on perceived duration also held when foreperiods ranged from 0.6 to 1.5 s (Experiments 5-7). Findings suggest that foreperiods appear to effectively modulate attention mechanisms necessary for temporal information processing. However, alternative explanations such as assimilation or compatibility effects cannot be totally discarded.     

Observing responses and discrimination learning

An operant response in the pigeon, whose performance results in exposure to the discriminative stimuli, is described and suggested as an experimental analogue for “observing.” Such an operant response is then used to explore the relationship between observing responses and discrimination learning in a variety of discrimination situations, of progressively increasing complexity. In general, the results support the contention that the development and maintainence of observing responses is closely related to the degree of differential behaviour manifested toward the discriminative stimuli. Certain modifications are suggested in the theoretical formulation underlying the concept of “observing responses.”     

Stimulus context and duration discrimination

The ability of human observers to discriminate duration was assessed in two types of tasks: (1) pulse tasks, in which the observer compared the duration of two brief increments in an ongoing sinusoid, and (2) gap tasks, in which the observer compared the duration of two brief interruptions in an ongoing sinusoid. Performance in these tasks was assessed in three different contexts: noise alone, noise plus continuous sinusoids, and noise plus continuous sinusoids chosen to induce a pitch segregation effect. Performance in the pulse task was independent of the changes in context; however, performance in the gap task changed as a function of context condition. There was a large decrement in the observers’ ability to discriminate duration when the stimulus ensemble induced the pitch segregation effect. The results are discussed in terms of the relationship between duration discrimination and stimulus variations which do not carry duration information.