Confidence and accuracy of near-threshold discrimination responses.

This article reports four subliminal perception experiments using the relationship between confidence and accuracy to assess awareness. Subjects discriminated among stimuli and indicated their confidence in each discrimination response. Subjects were classified as being aware of the stimuli if their confidence judgments predicted accuracy and as being unaware if they did not. In the first experiment, confidence predicted accuracy even at stimulus durations so brief that subjects claimed to be performing at chance. This finding indicates that subjects's claims that they are "just guessing" should not be accepted as sufficient evidence that they are completely unaware of the stimuli. Experiments 2-4 tested directly for subliminal perception by comparing the minimum exposure duration needed for better than chance discrimination performance against the minimum needed for confidence to predict accuracy. The latter durations were slightly but significantly longer, suggesting that under certain circumstances people can make perceptual discriminations even though the information that was used to make those discriminations is not consciously available.     

Two functions of verbal intergroup discrimination: identity and instrumental motives as a result of group identification and threat

In two studies, the authors examined the circumstances under which discrimination has an identity confirmation function or an instrumental function (instigating collective action). In Study 1, participants (N = 601) described a situation in which they had discriminated and then completed measures of functionality, group identification, and group threat. Both functions were predicted by group identification, whereas the instrumental function (but not identity confirmation) operated under group threat. In Study 2, "die-hard" soccer fans (N = 1,546) suggested soccer chants in reaction to either a group-reinforcing (own team scores) or group-threatening (other team scores) situation and rated the perceived functionality of the song. Although both of these conditions evoked discriminating songs, as predicted, these served a more identity-confirming function in the reinforcing situation but a more instrumental function (pepping up the team) in the threat situation. Results are discussed in terms of a contextual-functional model of intergroup discrimination.     

Discrimination of simultaneous and successive tones

A series of discrimination tasks involving simultaneous and successive presentation of pairs of piano notes was given to 27 Ss. The listeners exhibited less-than-perfect ability to “hear out” the component notes in simultaneous presentations. This finding, in agreement with the results of previous investigators, demonstrated the limitation of Ohm’s law of acoustical analysis. It was also found that changes in successive notes fOllowing simultaneous notes were discriminated more accurately than changes in simultaneous notes following successive notes. This was interpreted as suggesting that listeners are better able to analyze than to synthesize the components of complex tones.     

Some detrimental effects of using extra stimuli to guide learning in normal and autistic children

This study was designed to assess the effectiveness of using prompts (extra "guiding" stimuli) for teaching normal and autistic children. One group of normal children was pretrained on a color discrimination. Later, the colors were used as prompts (presented simultaneously with new training stimuli) to teach four new discriminations. Another group of normal children was trained on the same discriminations with a trial-and-error procedure (i.e., no prompting). A third group consisted of autistic children who were trained on these discriminations using the prompt procedure. Analyses of the results showed the following. (1) The trial-and-error group of normal children acquired more discriminations than the prompt group of normal children. (2) A comparison of the two prompt groups showed that the autistics failed to transfer from the prompt cue to the training cue more often than the normal children; rather, the autistics generally continued responding to the faded color cue. (3) Autistic and normal children who failed to acquire the discriminations when trained with a prompt procedure did acquire these discriminations when no prompt was used. That is, the results suggest that the presentation of an extra guiding stimulus was detrimental to the acquisition of training discriminations for all subjects, and particularly so far autistic children. Therefore, the common practice of providing extra guiding stimuli in proportion to the severity of the learning disorder may actually be harmful to the learning of new skills. Implications of these results for future research are discussed.     

Delayed stimulus control: recall for single and relational stimuli.

In a discrete-trial symbolic matching-to-sample procedure, pigeons' left-key responses were reinforced following presentation of one center-key sample, and right-key responses were reinforced following presentation of another. Recallability was measured by the difference between log ratios of left to right responses following each sample. In Experiment 1, samples were successively presented same or different wavelengths in the relational discrimination, or individual wavelengths in the single discrimination. The rate at which recallability decreased with increasing delay since sample presentation was the same for single and relational discriminations, but the initial level of performance differed, indicating that the relational discrimination was more difficult. In Experiment 2, recall functions for easy and difficult discriminations between individual wavelengths also differed in levels of initial performance but not in rate of decrement of recallability over time. Recall for stimuli differing in complexity may therefore reflect differences in discrimination difficulty.     

Visual search,complex backgrounds,mental counters,and eye movements

For 30 days, three Ss searched for 1, 5, or 10 targets (N), any one of which had to occur once (as in past research). twice, or four times (FREQ). The N=1 and N=5 items were subsets of N=10 items. When FREQ=1. Ss searched longer for 5 targets than for 1 or 10 targets. This nonintuitive result was due to (a) Ss searching for all 10 targets even at N=5, and (b) the reported “pop-out effect” of the 5 target items as well as the other 5 items in the N=10 set. When FREQ > 1, Ss could search for only 2-3 targets at once, because they could not keep mental counters on more items. The presence of a complex background merely added a constant to search time. The main change in eye movements, with 30 days practice, was to reduce greatly the number of eye fixations, thus suggesting an increase in the useful fidld of view and/or a change in search strategy. A speculative model, based upon two comparison processes, was suggested to explain the results.     

Discrimination of five-dimensional stimuli by pigeons: Limitations of feature analysis

Pigeons were trained to discriminate between stimuli constructed using five orthogonal two-valued features. The stimuli consisted of stylized monochrome drawings of seeds. Two different training procedures (conditional and simultaneous discrimination) were used. In the first two experiments, the discrimination required was between polymorphous categories, in which a positive stimulus was defined as one in which three or more of the five features took their positive values. Discrimination in both experiments was imperfect; the pigeons' behaviour only came under the control of a subset of the available features (one to three in Experiment 1, three or four in Experiment 2). In Experiment 3, single features had to be discriminated, while the remaining features varied. It was found that all five features of the “seed” stimuli could be discriminated, but one of them was exceptionally difficult. The results show that pigeons do not reliably use all the features available to them when making category discriminations. This casts doubts on feature analysis as a basis for the excellent performance pigeons show when required to discriminate between categories of natural objects.     

Stimulus-outcome interactions during instrumental discrimination learning by rats and humans

The associative structure mediating goal-directed action was investigated using congruent and incongruent conditional discriminations. The stimulus was the same as the outcome in each component of the congruent discriminations, whereas the stimulus of one component of the incongruent discriminations was the same as the outcome of the other component. Humans, but not rats, learned the congruent discrimination more rapidly than the incongruent discrimination, a difference that the authors attribute to the fact that outcome-response associations caused response conflict in the incongruent discrimination. Moreover, responding was resistant to outcome devaluation following incongruent, but not congruent, training, suggesting that both humans and rats adopted a stimulus-response strategy to resolve the incongruent discrimination.     

Age differences in discrimination of simulated single-formant frequency transitions

We studied auditory discrimination of simulated single-formant frequency transitions that resembled portions of certain speech consonants. Significant age differences in transition discrimination occurred; both children and older adults required larger acoustic differences between transitions for discrimination than did teenagers/young adults. Longer transitions were more easily discriminated than shorter transitions by all listeners, and there were no differences between discriminations of rising and falling transitions. Teens/young adults and older adults, but not children, required larger frequency differences to discriminate frequency transitions followed by a steady-state sound than for transitions alone. There were also age differences in discrimination of steady-state sounds. These developmental-perceptual differences may help explain why children and older adults who have good pure-tone sensitivity may experience difficulty in understanding speech.     

Perceptual dependence: Evidence for an internal threshold

Ss were asked to make two forced-choice discriminations on each trial: in Experiment I, they had to tell on which side of the display a latter pair appeared and whether or not its members were identical; in Experiment II, to say where the pair appeared and whether it consisted of Xs or Os; in Experiment III, to say where a letter appeared and whether it rhymed with E; and in Experiment IV, to say whether a letter pair was presented and whether it was a word. In Experiment III, and for some Ss in Experiment I, the second discrimination was dependent on the first; that is, when the S was wrong on the first, he performed at chance level on the second. In Experiment IV, when Ss indicated that nothing was presented (with confidence), they performed at chance level on the recognition task; thus, recognition was dependent upon some information about the detection task. It is argued that perceptual dependence implies that a threshold state, a state in which the S has no information, exists for the dependent discrimination. One explanation of dependence assumes mediation of the dependent discrimination by a processing stage which succeeds stages mediating the other task.     

Classical conditioning of autonomic fear responses is independent of contingency awareness

The role of contingency awareness in classical conditioning experiments using human subjects is currently under debate. This study took a novel approach to manipulating contingency awareness in a differential Pavlovian conditioning paradigm. Complex sine wave gratings were used as visual conditional stimuli (CS). By manipulating the fundamental spatial frequency of the displays, we were able to construct pairs of stimuli that varied in discriminability. One group of subjects was given an "easy" discrimination, and another was exposed to a "difficult" CS+ and CS-. A 3rd group was exposed to a stimulus that was paired with the unconditional stimulus (UCS) 50% of the time and served as a control. Skin conductance response (SCR) and continuous UCS expectancy data were measured concurrently throughout the experiment. Differential UCS expectancy was found only in the easy discrimination group. Differential SCRs were found in the easy discrimination group as well as in the difficult discrimination group, but not in the 50% contingency control. The difficult discrimination group did not exhibit differential UCS expectancy but did show clear differential SCR. These observations support a dual process interpretation of classical conditioning whereby conditioning on an implicit level can occur without explicit knowledge about the contingencies. The role of contingency awareness in classical conditioning experiments using human subjects is currently under debate. This study took a novel approach to manipulating contingency awareness in a differential Pavlovian conditioning paradigm. Complex sine wave gratings were used as visual conditional stimuli (CS). By manipulating the fundamental spatial frequency of the displays, we were able to construct pairs of stimuli that varied in discriminability. One group of subjects was given an "easy" discrimination, and another was exposed to a "difficult" CS+ and CS-. A 3rd group was exposed to a stimulus that was paired with the unconditional stimulus (UCS) 50% of the time and served as a control. Skin conductance response (SCR) and continuous UCS expectancy data were measured concurrently throughout the experiment. Differential UCS expectancy was found only in the easy discrimination group. Differential SCRs were found in the easy discrimination group as well as in the difficult discrimination group, but not in the 50% contingency control. The difficult discrimination group did not exhibit differential UCS expectancy but did show clear differential SCR. These observations support a dual process interpretation of classical conditioning whereby conditioning on an implicit level can occur without explicit knowledge about the contingencies.     

The evaluation and control of acoustical standing waves

Calibration of a standard pigeon box subsequently modified for use as an acoustical chamber in a frequency discrimination experiment revealed that the enclosure was not acoustically “flat”. Standing waves were detected at each of the six frequencies measured. To ascertain whether the maximum standing waves recorded (3.0 dB) could serve as an added or alternative cue for pigeons tested in the chamber on a frequency discrimination problem, pure-tone intensity difference thresholds were determined for two pigeons at 1.0, 2.0, and 3.0 KHz. The results of the experiment indicated that the smallest intensity difference detectable was 10.0 dB, a value that was 7.0 dB above the maximum standing wave measured in the box. These data suggest that the modified pigeon chamber is suitable to test pure-tone frequency discriminations in pigeons in the range of 1.0 to 3.0 KHz.     

Sequential letter and word recognition in deaf and hearing subjects

To examine the processing of sequentially presented letters of familiar and nonsense words, especially among Ss of vastly differing experience on sequential tasks, three groups of Ss were tested on letters of words spelled sequentially on an alphanumeric display and on letters of words fingerspelled. These were a deaf group (N=33) with little or no hearing and who varied in their fingerspelling ability; a staff group (N=12) who taught fingerspelling and were highly proficient; and a hearing group (N=19). Of principal interest was the finding that the hearing Ss did better on nonsense letter recognition, while the deaf group did better on word recognition. Word length was important except to the staff Ss on fingerspelled words, which also suggests that concentration on fingerspelling proficiency forces attention to the whole word and not its component letters. Hearing Ss, who are the group faced with an unfamiliar task, seemed to attend to each letter and hence had more difficulty with recognition of the longer unit.     

Visual and tactual form discrimination: Psychophysical comparison within and between modalities

Intermodal perceptual equivaience was investigated, using visual and tactual oddity discrimination and cross-modal matching-to-sample tasks. Four groups of Ss were presented with 100 problems made up of randomly derived forms from five levels of sidedness. The same quadratic relationship was observed for all tasks as a function of complexity, with optimal performance at eight sides. Comman information utilization, as indicated by intercorrelations of performance variables and by correlational analyses with differences in form measures, was not as pronounced within side classes. Evidence concerning the nature of pattern-feature usage in discrimination was obtained from graphical analyses.     

The elusive tradeoff: Speed vs accuracy in visual discrimination tasks

Theoretical models for choice reaction time and discrimination under time pressure must account for Ss’ ability to trade accuracy for increased speed. The fast guess model views these tradeoffs as different mixtures of “all-or-none” strategies, while incremental models assume they reflect different degrees of thoroughness in processing the stimulus. Three experiments sought tradeoffs for difficult visual discriminations, using explicit payoffs to control and manipulate pressures for speed and accuracy. Although guessing was pervasive, the simple fast guess model could be rejected; Experiments II and III obtained tradeoffs even when fast guesses were purged from Ss’ data. Tradeoff functions fit by several formulations revealed: (1) slower rates of increase in accuracy for more similar stimuli, and (2) substantial “dead times” (80–100 msec slower than detection times) before discrimination responses could exceed chance accuracy. Errors were sometimes faster and sometimes slower than correct responses (depending on S’s speed-accuracy trade); the latter effect may reflect a ceiling on S’s achievable accuracy. A final discussion examines implications of the results for models of discrimination under time pressure; it suggests modifications in present models, focusing on the random walk model, and describes an alternative “deadline” model.     

Frequency and coding responses in verbal discrimination learning

Ss were given a verbal discrimination task where correct and incorrect stimuli appeared in one, two. or four different pairs in a within-Ss design. For a group tested with the usual anticipation procedure, correct repetitions helped and incorrect repetitions hurt performance. The pattern of results suggested that frequency is a salient cue in verbal discrimination learning but that coding or paired-associate processing may occur at the same time. Data from a second group of Ss for which frequency was a less salient cue gave more direct evidence for coding.     

Why are artificial polymorphous concepts so hard for birds to learn?

Stimulus sets defined in terms of artificial polymorphous concepts have frequently been used in experiments to investigate the mechanisms of discrimination of natural concepts, both in humans and in other animals. However, such stimulus sets are frequently difficult for either animals or humans to discriminate. Properties of artificial polymorphous stimulus sets that might explain this difficulty include the complexity of the individual stimuli, the unreliable reinforcement of individual positive features, attentional load, difficulties in discriminating some stimulus dimensions, memory load, and a lack of the correlation between features that characterizes natural concepts. An experiment using chickens as subjects and complex artificial visual stimulus sets investigated these hypotheses by training the birds in discriminations that were not polymorphous but did have some of the properties listed above. Discriminations that involved unreliable reinforcement or high attentional load were found to approach the difficulty of polymorphous concept discriminations, and these two factors together were sufficient to account for the entire difficulty. The usual kind of artificial polymorphous concept may not be a good model for natural concepts as they are perceived and discriminated by birds. A RULEX account of natural concept learning may be preferable.     

Why are artificial polymorphous concepts so hard for birds to learn?

Stimulus sets defined in terms of artificial polymorphous concepts have frequently been used in experiments to investigate the mechanisms of discrimination of natural concepts, both in humans and in other animals. However, such stimulus sets are frequently difficult for either animals or humans to discriminate. Properties of artificial polymorphous stimulus sets that might explain this difficulty include the complexity of the individual stimuli, the unreliable reinforcement of individual positive features, attentional load, difficulties in discriminating some stimulus dimensions, memory load, and a lack of the correlation between features that characterizes natural concepts. An experiment using chickens as subjects and complex artificial visual stimulus sets investigated these hypotheses by training the birds in discriminations that were not polymorphous but did have some of the properties listed above. Discriminations that involved unreliable reinforcement or high attentional load were found to approach the difficulty of polymorphous concept discriminations, and these two factors together were sufficient to account for the entire difficulty. The usual kind of artificial polymorphous concept may not be a good model for natural concepts as they are perceived and discriminated by birds. A RULEX account of natural concept learning may be preferable.     

Reality versus suggestion: pseudomemory in hypnotizable and simulating subjects

Assigned hypnotizable (N = 56) and simulating Ss (N = 44) to 1 of 4 conditions: heard a phone ring and conversation, received a suggestion to hear a phone ring and conversation, received a suggestion and heard a phone ring and conversation, or neither heard a phone nor received a suggestion. Hypnotizable Ss successfully discriminated objective events from suggested sources of input. When Ss received a suggestion to hear a phone ring, only 11.5% indicated it actually rang in their open-ended reports; in response to a forced-choice question, none did so. In spontaneous reports, none of the hypnotizable Ss who heard a phone ring indicated it was suggested; only one did so in response to a forced-choice item (vs. 2 simulators). In the no-phone/no-suggestion condition, more simulators than hypnotizable Ss indicated that a phone rang or was suggested.     

Memory for modality of presentation: Within-modality discrimination

Two experiments demonstrated that Ss are capable of making within-modality memory discriminations in both visual and auditory modalities. In Experiment I Ss studied mixed lists of pictures and labels representing common objects and were subsequently required to judge whether the original presentation was pictorial or verbal The high level of performance achieved on this task was unaffected by degree of categorical relatedness of items within method of presentation or by instructions to produce visual images when items were presented verbally. In Experiment II Ss demonstrated the ability to remember whether a sentence was originally presented by a male or a female speaker. Some strategies by which within-modality discrimination in memory might be accomplished are discussed.