SDT analysis of binary decisions and sensory intensity ratings to noxious thermal stimuli

During three sessions, each of 24 Ss responded to noxious thermal stimuli, using the following judgments: binary decision, S responded “high” or “low”; sensory intensity rating, S rated his sensory experience along a thermal intensity continuum; and concurrent report, S’s binary decision was followed by an intensity rating. The binary-decision d’ was significantly higher than the rating d′, suggesting that Ss could not maintain multiple thermal criteria in a consistent fashion. The criteria for pain obtained with single and concurrent intensity rating judgments did not differ. These results suggest that the most efficacious and valid method for the study of experimental pain is to obtain concurrent responses, and to use binary decisions to compute d’ and sensory intensity ratings to locate S’s criterion for reporting pain.     

Withdrawing attention at little or no cost: Detection and discrimination tasks

We used a concurrent-task paradigm to investigate the attentional cost of simple visual tasks. As in earlier studies, we found that detecting a unique orientation in an array of oriented elements (“pop-out”) carries little or no attentional cost. Surprisingly, this is true at all levels of performance and holds even when pop-out is barely discriminable. We discuss this finding in the context of our previous report that the attentional cost of stimulus detection is strongly influenced by the presence and nature of other stimuli in the display (Braun, 1994b). For discrimination tasks, we obtained a similarly mixed outcome: Discrimination of letter shape carried a high attentional cost whereas discrimination of color and orientation did not. Taken together, these findings lead us to modify our earlier position on the attentional costs of detection and discrimination tasks (Sagi & Julesz, 1985). We now believe that observers enjoy a significant degree of “ambient” visual awareness outside the focus of attention, permitting them to both detect and discriminate certain visual information. We hypothesize that the information in question is selected by a competition for saliency at the level of early vision.     

Recovering stimuli from memory: A statistical method for linking discrimination and reproduction responses

Investigations of sensory memory have often relied on discrimination processes: participants judge whether a reference stimulus is identical to a remembered stimulus. Recently, investigators have used response modes in which participants directly reproduce stimuli. Findings using reproduction tasks have suggested new ways of thinking about biases that pervade psychophysics. To allow an assessment of whether results obtained using reproduction responses persevere for discrimination tasks, this paper presents a statistical model that links the two approaches. The model uses the pattern of discrimination judgements to estimate parameters that represent the means and standard deviations that would have occurred under a reproduction task. An analysis of stimuli that have been previously studied using reproduction responses illustrates the method. Simulations investigate bias and efficiency, large‐sample confidence intervals and the performance of likelihood‐ratio tests of the adequacy of special submodels.     

A multidimensional scaling analysis of vowel discrimination in humans and monkeys

Multidimensional scaling (MDS) was used to compare perceptual maps for 10 synthetic English vowels in humans and Old World monkeys (Macaca fuscata andCercopithecus albogularis). Subjects discriminated among the vowels using a repeating background procedure, and reaction times were submitted to an MDS analysis to derive measures of perceived similarity. The dimensions that emerged related to the frequencies of the first(F1), second(F2), and third(F3) formants. Human data indicated a good match to previous MDS studies using rating procedures or confusion matrices: The dominant dimension mapped onto vowelF2, the phonetically most important formant, and the second and third dimensions mapped ontoF1 andF3, respectively.For monkeys, equal weightings occurred forF1 andF2, andF3 was not clearly represented. Monkey sensitivity to the formants appeared to relate to formant amplitudes. If monkeys are giving an accurate representation of the psychoacoustic relations among the formants, then our human results suggest that species-specific mechanisms, reflecting the salience of the phonetic feature of advancement, may contribute to vowel coding in humans.     

Unique transitions between stimuli and responses in SRT tasks: Evidence for the primacy of response predictions

The present experiments aimed at separating the impact stimulus and response predictions have on serial learning and performance in SRT tasks. In Experiment 1, a unique transition between two of four responses in an otherwise random response sequence was triggered by ambiguous stimulus transitions, allowing local response predictions but no stimulus predictions. The data indicated explicit transition knowledge and strong performance benefits. In Experiments 2 and 3, unique transitions between two of four stimuli in otherwise random stimulus sequences allowed local stimulus predictions under conditions of ambiguous response transitions. The data indicated fragmentary explicit transition knowledge but no performance effects. Experiments 4a and 4b reveal that the inefficacy of the unique stimulus transitions in Experiments 2 and 3 was presumably due to the fact that the stimuli differed with respect to conjunctions of response relevant and response irrelevant features which participants did not have to attend. However, although in Experiments 4a and 4b unique transitions between response relevant stimuli were applied, substantial explicit transition knowledge but only marginal performance effects resulted. It is argued i) that in SRT tasks learning mechanisms are addressed that primarily strive for reliable predictions of forthcoming responses and ii) that for these mechanisms to work the predictors have to be attended. Response transitions are easily learned and used because both criteria are fulfilled. In contrast, pure stimulus transitions are learned only if the predictive stimuli are attended, and learned stimulus transitions become effective only to the extent that the predicted stimuli specify the required responses.     

Emergent conditional discrimination in children: Matching to compound stimuli

This study reports two experiments that first taught preschool children identity-matching to compound sample and compound comparison stimuli. A compound stimulus consisted of a colour and a form superimposed on one another. Test sessions assessed whether children related the form and colour elements of a particular compound stimulus. The test for this was matching to sample in which an arbitrary conditional discrimination was required. A majority of the children selected the correct colour comparison in the presence of each form sample. The children also showed the reverse sample-comparison relations: they matched form comparisons to the corresponding colour samples, respectively. In the context of these arbitrary relations, new colours were paired with the form elements of the samples (Experiment 1), and new form elements were paired with the colour elements of the comparisons (Experiment 2). Subsequent tests assessed whether the new stimulus elements had control over responding when presented as single samples or comparisons. Test results showed that most subjects were able to relate the new stimulus elements to the corresponding colour and form elements, respectively. The study demonstrated that matching to compound stimuli in training and testing conditionsMaygenerate conditional relations between the individual stimulus elements.     

Conditional discrimination and equivalence relations: A theoretical analysis of control by negative stimuli

A detailed analysis is presented of the ways in which control by the negative stimulus in two-comparison conditional discriminations may be expected to affect the outcome of tests for the properties of equivalence relations. Control by the negative stimulus should produce the following results: (a) no observable effect on symmetry tests; (b) reflexivity test results should look like “oddity” rather than “identity”; and (c) transitivity tests that involve an odd number of nodes should yield results that are 100% opposite to tests that involve an even number of nodes. The analysis also considers the effects of variation in the type of comparison-stimulus control between and within baseline conditional discriminations. Methods are suggested for experimentally regulating the type of control, and for verifying the predictions that the analysis generates. If suggested experiments continue to support the analysis, investigators who use two-comparison conditional discriminations to study equivalence relations will either have to control explicitly whether the positive or the negative comparison governs their subjects' choices, or they will have to abandon two comparisons and use three or more comparisons instead.     

Effects of differences between stimuli, responses, and reinforcer rates on conditional discrimination performance

In a discrete-trial conditional discrimination procedure, 4 pigeons obtained food reinforcers by pecking a key with a short latency on trials signaled by one stimulus and by pecking the same key with a long latency on trials signaled by a second stimulus. The physical difference between the two stimuli and the temporal separation between the latency values required for reinforcement were varied factorially over four sets of conditions, and the ratio of reinforcer rates for short and long latencies was varied within each set of conditions. Stimulus discrimination varied directly with both stimulus and response differences and was unaffected by the reinforcer ratio. Sensitivity to reinforcement, estimated by generalized-matching-law fits to the data within each set of conditions, varied directly with the response difference but inversely with the stimulus difference arranged between sets of conditions. Because variations in stimulus differences, response differences, and reinforcer differences did not have equivalent effects, these findings question the functional equivalence of the three terms of the discriminated operant: antecedent stimuli, behavior, and consequences.     

Behold the wrath: Psychophysiological responses to facial stimuli

The complex musculature of the human face has been shaped by natural selection to produce gestures that communicate information about intentions and emotional states between senders and receivers. According to the preparedness hypothesis, different facial gestures are differentially prepared by evolution to become associated with different outcomes. As attested by psychophysiological responses in Pavlovian conditioning experiments, expressions of anger and fear more easily become signals for aversive stimuli than do expression of happiness. Consistent with the evolutionary perspective, the superior conditioning to angry faces is stronger for male than for female faces, for adult than for child faces, and for faces directed toward the receiver rather than directed away. Furthermore, it appears to be primarily located in the right cerebral hemisphere. The enhanced autonomic activity to angry faces signaling electric shock is not mediated by conscious cognitive activity, but is evident also when recognition of the facial stimulus is blocked by backward masking procedures. Similarly, conditioned responses can be established to masked angry, but not to masked happy faces. Electromyographic measurement of facial muscle activity reveals a tendency for emotional facial expression to rapidly and automatically elicit its mirror image in the face of the receiver, typically accompanied by the appropriate emotional experience. The research reviewed in this paper supports the proposition that humans have been evolutionarily tuned to respond automatically to facial stimuli, and it is suggested that such early automatic reactions shape the subsequent conscious emotional processing of the stimulus.The responsibility for this paper is shared equally between the authors. The research reviewed in the paper has been supported by separate grants to both authors from the Swedish Council for Research in the Humanities and Social Sciences, The Swedish Council for the Coordination and Planning of Research, and the Bank of Sweden Tercentennial Fund.     

Comparative scaling of unidimensional discrimination and similarity data

Scales constructed from paired-comparison designs under Thurstone's Case V model are discussed in relation to those derived from similarity data by means of the Unilateral Law of Comparative Judgment [3]. Factors inherent in the triadic similarity task are then considered with respect to scale invariance across experimental designs. Illustrative data, although revealing the influence of these factors upon similarity response consistency, indicate the similarity scale to be somewhat robust to their biasing effects.This research was supported in part by National Institute of Mental Health Grant MH-04439-05.     

Behavior simultaneously maintained by both presentation and termination of noxious stimuli

Lever pressing by two squirrel monkeys was maintained under a 3-minute variable-interval schedule of response-produced electric-shock presentation. At the same time, responding on a second lever was maintained under a 3-minute fixed-interval schedule of termination of the shock-presentation schedule and shock-correlated stimuli. Under the termination schedule, the first response after a 3-minute period produced a 1-minute timeout, during which no events occurred and responding had no scheduled consequence. Relatively high and constant rates of responding were maintained on the lever where responding produced shock. Lower rates and positively accelerated patterns of responding occurred on the lever where responding terminated the shock schedule. Thus, responding was simultaneously maintained by presentation of an event and by termination of a stimulus associated with that event. Rates and patterns of responding on each lever were reversed when the schedules arranged on each lever were reversed on two occasions. When shock intensity was increased from 0 to 10 mA, responding maintained both by presentation of shock and by termination of the shock schedule increased, but responding maintained by shock presentation increased to a greater extent. Positive and negative reinforcement, usually regarded as separate behavioral processes involving different events, can coexist when behavior is controlled by different contingencies involving the same event.     

Emotional and autonomic responses to visual traumatic stimuli

A fine-grain analysis of autonomic responses are presented with the purpose of extending the conclusions from a previously published paper (Christianson & Nilsson, 1984) on emotional and memorial responses to traumatic visual stimuli. Control subjects were presented with a series of 18 slides of neutral faces, whereas the experimental subjects were presented with six slides of horrible facial injuries in positions 7–12, interspersed between six slides of neutral faces in the beginning, and six slides of neutral faces at the end of the series. The time course of heart rate (HR) and skin conductance (SC) during stimulus presentation was recorded. These data showed an initial pattern of increase in SC, but not in HR. This pattern was subsequently replaced by a combined increase in both SC and HR. The results are discrepant to previous work and are interpreted as effects of not informing the subjects about the gruesome slides to be presented.     

Conditional discrimination and equivalence relations: Control by negative stimuli

Three adult subjects were taught the following two-sample, two-comparison conditional discriminations (each sample is shown with its positive and negative comparison, in that order): A1-B1B2, A2-B2B1; B1-C1C2, B2-C2C1; and C1-D1D2, C2-D2D1. A teaching procedure was designed to encourage control by negative comparisons. Subjects were then tested for emergent performances that would indicate whether the baseline conditional discriminations were reflexive, symmetric, and transitive. The tests documented the emergence of two classes of equivalent stimuli: A1, B2, C1, D2 and A2, B1, C2, D1. These were the classes to be expected if the negative comparisons were the controlling comparisons in the baseline conditional discriminations. The negative comparisons, however, were not the comparisons that subjects were recorded as having chosen in the baseline conditional discriminations. Differential test results confirmed predictions arising from a stimulus-control analysis: In reflexivity tests (AA, BB, CC, DD), subjects chose comparisons that differed from the sample; one-node transitivity (AC, BD) and "equivalence" (CA, DB) tests also yielded results that were the opposite of those to be expected from control by positive comparisons; symmetry tests (BA, CB, DC), two-node transitivity (AD) tests, and two-node "equivalence" (DA) tests yielded results that were to be expected from control by either positive or negative comparisons.     

Contribution of thermal cues to material discrimination and localization

The objective of these two experiments was to determine the role of thermal cues in material discrimination and localization, using materials that spanned a range of thermal properties. In the first experiment, the subjects were required to select the cooler of two materials presented to the index fingers. In the second, the finger that was in contact with a material that was different from that presented to the other two fingers on the same hand had to be identified. The results indicated that the subjects were able to discriminate between materials, using thermal cues, when the differences in their thermal properties were large. The changes in skin temperature when the fingers were touching the materials were, however, smaller than those predicted by the theoretical model. The ability to localize the thermal changes when three fingers on the same hand were stimulated was poor and depended on both the thermal properties of the target and the distractor materials.     

Pupillary responses to pictures and descriptions of sex-stereotyped stimuli

An attempt was made to replicate Hess and Polt's (1960) report of sex differences in pupillary responses to sex-stereotyped pictures. Some methodological refinements were used that seem desirable for future studies. College men and women were either shown or told they would be shown pictures of a semi-nude man, a semi-nude woman, a baby, and a landscape. With resting pupil size as covariate, a three-factor analysis of covariance did not show sex differences in response to visually presented stimuli. Men responded more to verbal than visual mode of presentation and more than women to verbal stimuli. Contrary to previous results, men responded as much or more than women to verbal or visual presentation of baby stimuli. The verbal or anticipatory mode seems to be at least as sensitive as the visual and eliminates problems of control of visual materials.