A sequential theory of psychological discrimination

A theory of discrimination which assumes that subjects compare psychological values evoked by a stimulus to a subjective referent is proposed. Momentary differences between psychological values for the stimulus and the referent are accumulated over time until one or the other of two response thresholds is first exceeded. The theory is analyzed as a random walk bounded between two absorbing barriers. A general solution to response conditioned expected response times is computed and the important role played by the moment generating function (mgf) for increments to the random walk is examined. From considerations of the mgf it is shown that unlike other random walk models [Stone, 1960; Laming, 1968] the present theory does not imply that response conditioned mean correct and error times must be equal. For two fixed stimuli and a fixed referent it is shown that by controlling values of response thresholds, subjects can produce Receiver Operating Characteristics similar or identical to those predicted by Signal Detection Theory, High Threshold Theory, or Low Threshold Theory.     

Effect of simultaneous auditory stimulation on vibrotactile thresholds

Vibrotactile thresholds were determined at 250 and 400 Hz in the presence of (1) the sounds emitted by the vibrator, (2) continuous tonal or narrow-band masking noise, or (3) a pulsed tone synchronized with the vibrator signal. The measure of a cross-modality effect was the threshold shift occurring between each condition and the control condition, in which earmuff silencers eliminated the vibrator sounds. Continuous tones or noise had no effect upon vibrotactile thresholds. However, auditory signals synchronized with the vibrator signals did significantly elevate vibrotactile thresholds.     

Vibrotactile vigilance: The effects of costs and values on signals

Vibrotactile vigilance behavior was examined for the effects on signal detection performance of placing costs on misses and false detections and a positive value on the correct detection of a signal. Analyses over time showing that the frequencies of correct detection and false detection of signals decreased, while response times increased, indicated that increased costs for misses and false alarms lead to poorer correct detection performance, while the value placed on the correct detection of a signal had little effect. The d’ statistic of signal detection theory was invariant with both signal costs and time, while β varied with both factors.These results imply that the performance decrement during a vigil was due to an increased strictness in the criterion (β) the S set for deciding whether or not a signal was present. The cost factors were effective in manipulating performance during the watch by causing changes in the S’s decision criteria. Findings from this study clearly support those predicted by the “Decision Theory” of Swets, Tanner, and Birdsall (1961); this is suggested as perhaps being the best available basis for a theory of vigilance at this time.     

Colavita dominance effect revisited: the effect of semantic congruity

To investigate the effect of semantic congruity on audiovisual target responses, participants detected a semantic concept that was embedded in a series of rapidly presented stimuli. The target concept appeared as a picture, an environmental sound, or both; and in bimodal trials, the audiovisual events were either consistent or inconsistent in their representation of a semantic concept. The results showed faster detection latencies to bimodal than to unimodal targets and a higher rate of missed targets when visual distractors were presented together with auditory targets, in comparison to auditory targets presented alone. The findings of Experiment 2 showed a cross-modal asymmetry, such that visual distractors were found to interfere with the accuracy of auditory target detection, but auditory distractors had no effect on either the speed or the accuracy of visual target detection. The biased-competition theory of attention (Desimone & Duncan Annual Review of Neuroscience 18: 1995; Duncan, Humphreys, & Ward Current Opinion in Neurobiology 7: 255–261 1997) was used to explain the findings because, when the saliency of the visual stimuli was reduced by the addition of a noise filter in Experiment 4, visual interference on auditory target detection was diminished. Additionally, the results showed faster and more accurate target detection when semantic concepts were represented in a visual rather than an auditory format.     

Effects of the menstrual cycle on vibrotactile sensitivity

Psychophysical thresholds for the detection of vibration delivered to the thenar eminence of the right hands of young males and females were measured every other day for 30–34 days. The frequency of the vibratory stimulus was either 15 or 250 Hz. The sinusoidal stimuli applied through a 3.0-cm² contactor were 700 msec in duration and had rise-fall times of 25 msec. Stimulus amplitude was measured with a calibrated accelerometer mounted on the moving element of the vibrator. Data were plotted as a function of successive days in the menstrual cycle. Thresholds for detecting the 15-Hz stimulus did not change significantly, whereas thresholds for detecting the 250-Hz stimulus varied significantly over the menstrual cycle. The 250-Hz threshold became progressively lower as subjects approached the onset of menstruation. After the onset of menstruation, the 250-Hz threshold gradually increased, reaching a maximum value approximately 12 or 13 days later. Soon after the 12th or 13th day of the cycle, the threshold again began to decline and continued to decline until the onset of the next menstrual cycle. The thresholds of women taking birth control pills did not change systematically over the testing period.     

Operant methods for mouse psychoacoustics

Tone detection thresholds for a 10-kHz tone in NMRI mice were determined in psychoacoustic experiments using both a constant-stimuli procedure and a two-down/one-up adaptive-tracking procedure in the same subjects and applying identical threshold criteria (70.7% response probability). Constant-stimuli thresholds were on average 24 dB lower than adaptive-tracking thresholds, and there was a trend indicating that constant-stimuli thresholds were less variable than adaptive-tracking thresholds. Furthermore, in the constant-stimuli procedure the number of trials constituting the psychometric function could be reduced from 100 to 50 trials without a large loss of accuracy of threshold determination. In the constant-stimuli procedure, the threshold value was affected by the threshold criteria. The lowest and least variable constant-stimuli thresholds were obtained by applying signal detection theory and a criterion ofd′=1. Thus, the constant-stimuli procedure in combination with signal detection theory appears to be better suited than the adaptive-tracking procedure to determine auditory sensory thresholds.     

Critical flicker fusion in primary degenerative dementia of the alzheimer’s type (PDDAT): Clinical implications (II)

Critical Flicker Fusion Threshold (CFFT) and the difference between fusion and flicker thresholds were examined in 23 female and three male patients with Primary Degenerative Dementia of the Alzheimer’s type (PDDAT). The control group consisted of age, sex, and occupational class-matched, normal volunteers. Patients had a mean age of 81.7 years ±6.05 (range 67–89); diagnosis was based on DSM-IIIR criteria. The psychophysical method of limits was used to measure three ascending (fusion) and three descending (flicker) means the average being the CFFT. Both the CFFT and the flicker thresholds were able to distinguish between patients and volunteers at a high level of statistical significance (t=2.054, df=50, p<0.0018 and t=?4.903, df=50, p<0.0000 respectively). Sixty-five percent of patients had CFFT scores below 1.96 SD of the volunteer CFFT mean and 85 percent of patients had flicker thresholds below 1.96 SD of the volunteer flicker mean. The fusion thresholds were not significantly different in the two groups but the fusion thresholds were significantly greater than the flicker thresholds in patients (t=5.617, df=25, p<0.0000). One interpretation of the results in that patients with PDDAT have a significant reduction in the sensitivity of the Central Nervous System to suprathreshold flicker. Accurate diagnosis of early PDDAT (probable Alzheimer’s disease) continues to remain one of the most difficult areas in dementia research. The use of simple quantitative measures such as CFFT may have an important role to play in the overall assessment of patients with PDDAT.     

Taste thresholds in college-age smokers and nonsmokers

Taste detection thresholds were measured for NaCl and Dulcin and recognition thresholds for NaCl, sucrose, HCl, and QSO₄ in college-age smokers and nonsmokers. There were no consistent differences in thresholds for any compound between smokers and nonsmokers.     

The Pavlovian basis of reciprocal inhibition therapy

While there is a slight disagreement between Wolpe’s views and Pavlov’s statements concerning the application of experimental psychology to the study of psychiatry, Wolpe indicates that he owes much to Pavlov. A Pavlovian analysis of therapy by reciprocal inhibition, which includes the physiological constructs as well as Pavlovian methodology, will increase our understanding of Reciprocal Inhibition therapy. The major techniques of Reciprocal Inhibition therapy are discussed in the terms of Pavlovian method and theory. Desensitization based on systematic relaxation appears to be effective because the excitatory stimulus is presented when the subject’s cortex is predominantly in an inhibitory state while relaxed. Assertive training relies mainly on building up the excitatory process by use of the second signal system. Thought-stopping is analogous to the external inhibition procedure with the use of the second signaling system as the “extra” stimulus. Deductions from Pavlov’s typology predict that an excitable subject will be difficult to desensitize and somewhat easier to train in assertive behavior and thought-stopping. Some implications of relating Pavlovian method and theory to Reciprocal Inhibition therapy are discussed.     

Comparison of child and adult vibrotactile thresholds as a function of frequency and duration

Psychophysical thresholds for the detection of sinusoidal vibration of the thenar eminence of the hand were determined for children and adults. The subjects in the child group were between 8 and 11 years old, and the adults were between 20 and 39 years old. Measurements were made for vibration frequencies ranging from 18 to 700 Hz and stimulus durations ranging from 28 to 1,000 msec. For both children and adults, thresholds were a Il-shaped function of stimulus frequency. However, the exact form of the function was influenced by the age of the subjects. At frequencies above 200 Hz, thresholds were virtually identical for children and adults, but below this frequency children were more sensitive than adults. This finding, in combination with known changes in the anatomy of the Pacinian corpuscle with age, is in agreement with a filter model of this cutaneous receptor. Furthermore, variation of stimulus duration resulted in data in agreement with the theory that two classes of mechanoreceptors, Pacinian and non-Pacinian, mediate the perception of vibration.     

A console for the interactive on-line administration of psychological tests

A computer controlled console for on-line psychological testing of psychiatric patients is described. The Peabody Picture Vocabulary Test and the Kelly Role Construct Repertory Test are computer administered using three visual, one auditory, and two response modes. Test data are analyzed, interpreted, and incorporated into a program-written psychological report. Benefits and other applications from such a system are noted.     

Observers detecting a signal in two multiple observation tasks

Signal detection theory (SDT) is tested against a high threshold and a low threshold theory for two kinds of unusual tasks. In the first, the detection of the signal uses the central level of information processing; in the second, the lack of information originates in the stimulus itself rather than in the sensory organs' limitations. The observation is repeated a fixed number of times for the two tasks, and the observed integration of successive information is compared with predictions derived from the SDT and from threshold theories. All results strongly support the SDT which can thus be considered as a general model for risky binary decision-making insofar as these experiments are representative. This would be an argument to replace the classical analysis of the performance in terms of time and number of errors by a new analysis in terms of capability and strategy. The data show how the subjects are more selective for detecting the signal when the task is more difficult, and at the beginning and the end of a series of presentations. The organization of the decision-criteria of the rating-procedure varies with the difficulty of the condition, and with the number of observations in order to allow the subject to discriminate between likelihood ratios which become more precise.     

Sensory Extinction: A procedure for eliminating self-stimulatory behavior in developmentally disabled children

This study was designed to investigate the role of sensory reinforcement in the motivation of self-stimulation. If self-stimulatory behavior is maintained by its sensory consequences, such as the proprioceptive, auditory, or visual stimulation it produces, then such behavior should extinguish when those sensory consequences are not permitted. The present study introduces a new procedure, Sensory Extinction, in which certain sensory consequences are masked or removed, to examine whether self-stimulation is operant behavior maintained by sensory reinforcement. The effectiveness of Sensory Extinction was assessed by a reversal design for each of three autistic children, and the results showed the following. First, self-stimulation reliably extinguished when a certain sensory consequence was removed, then increased when that consequence was permitted. This was replicable within and across children. Second, different Sensory Extinction procedures were required for different self-stimulatory behaviors, since the sensory reinforcers supporting them were idiosyncratic across children. Finally, regarding clinical gains, the data suggest that Sensory Extinction may be a relatively convenient and rapid alternative for the treatment of self-stimulation. The present findings extend the efficacy of extinction as a behavior-modification technique to instances in which the reinforcer is purely sensory. The implications of these results for the treatment of other forms of deviant behavior are discussed.     

Sex differences in fetal habituation

There is some evidence for sex differences in habituation in the human fetus, but it is unknown whether this is due to differences in central processing (habituation) or in more peripheral processes, sensory or motor, involved in the response. This study examined whether the sex of the fetus influenced auditory habituation at 33 weeks of gestation, and whether this was due to differences in habituation or in the sensory or motor components using a set of four experiments. The first experiment found that female fetuses required significantly fewer stimulus presentations to habituate than males. The second experiment revealed no difference in the spontaneous motor behaviour of male and female fetuses. The third experiment examined auditory intensity thresholds for the stimuli used to habituate the fetus. No differences in thresholds were found between males and females, although there was inter-individual variability in thresholds. A final experiment, using stimuli individualized for that particular fetus' auditory intensity threshold, found that female fetuses habituated faster than males. In combination, the studies reveal that habituation in the human fetus is affected by sex and this is due to a difference in central 'information processing' of the stimuli rather than peripheral aspects of the response. It is argued that male and female fetuses present different neurobehavioural developmental trajectories, with females more advanced at 33 weeks than males. This study suggests that research examining prenatal behaviour should consider the factor of fetal sex. This may be particularly pertinent where there is an intention to use the results diagnostically.     

Personality and conditioning: Factors of classical CR acquisition and extinction and their relationship to personality types

Anumber of psychophysiological, cognitive and personality measures, and classical appetitive and aversive SR acquisition and extinction rates were taken from a sample of 25 male undergraduate volunteers. Principal Components Analysis of the data revealed general acquisition and extinction factors which were indexed by the psychophysiological variables. Regression analyses showed additionally that Eysenck’s E-I dimension predicts both acquisition and extinction rates, and that imagery may be an important mediational variable in CR acquisition.     

The skill of recognizing musical structures

In three experiments, musicians and nonmusicians were compared in their ability to discriminate musical chords. Pairs of chords sharing all notes in common or having different notes were played in succession. Some pairs of chords differed in timbre independent of their musical structures because they were played on different instruments. Musicians outperformed nonmusicians only in recognizing the same chord played on different instruments. Both groups could discriminate between instrument timbres, although musicians did slightly better than nonmusicians. In contrast, with chord structures not conforming to the rules of tonal harmony, musicians and nonmusicians performed equally poorly in recognizing identical chords played on different instruments. Signal detection analysis showed that musicians and nonmusicians set similar criteria for these judgments. Musicians' superiority reflects greater sensitivity to familiar diatonic chords. These results are taken as evidence that musicians develop perceptual and cognitive skills specific to the lawful musical structures encountered in their culture's music. Nonmusicians who lack this knowledge based their judgments on the acoustical properties of the chords.     

Adding sound to lipread lists: The effects on serial recall of adding an auditory pulse train and a pure tone to silently lipread lists

These investigations examined subjects’ serial recall of lipread digit lists accompanied by an auditory pulse train. The pulse train indicated the pitch of voiced speech (buzz-speech) of the seen speaker as she was speaking. As a purely auditory signal, it could not support item identification. Such buzz-speech recall was compared with silent lipread list recall and with the recall of buzz-speech lists to which a pure tone had been added (buzz-and-beep lists). No significant difference in overall accuracy of recall emerged for the three types of lipread list; however, there were significant differences in the shape of the serial recall function for the three list types. Recency characterized the silent and the buzz-speech lists, and these lists differed in their varying susceptibilities to a range of speechlike suffixes. By contrast, adding a pure tone to a buzz-speech list (buzz-and-beep) produced little recency and no further recall loss as a function of suffix type. We discuss these effects with reference to the contrast betweensensory-similarity and speechlikeness accounts of auditory recency and suffix effects. Sensory similarity accounts cannot capture the effects reported here, but processing in a speech mode (buzz-and-beep) need not always lead to recency effects like those resulting from clearly heard or lipread lists.     

The relation of field dependence to signal detection while imaging

Twelve field-dependent (FD) and 12 field-independent (FI) males were administered 260 trials of a signal detection task in four phases. Signal type (auditory, visual, or no signal) was crossed with four sets of imaging treatments (pure visual representations, pure sounds without visual counterparts, and two sets representing sounds with visual counterparts). Detection of a signal in isolation was 90% accurate, as was the detection of no signal while imaging. Cross-modality imaging interfered with detection of the stimulus but to a significantly lesser extent than did same-modality imaging. In all detection/imaging treatments, FIs were significantly more sensitive to the signal than were FDs; however, FDs and FIs did not differ in accuracy of detecting isolated signals. The results are discussed in terms of the commonalities shared by perception and imaging as they appear in the Perky effect and cognitive style.     

Invalid results from the method of constant stimuli

The Method of Constant Stimuli was shown to produce constant errors in the direction expected by E. In an experiment, 89 Ss compared variable lines with a standard, each S producing a psychometric function and Point of Subjective Equality (PSE). Four groups differed in the particular range of variable stimuli used; whether the stimuli averaged longer or shorter than the standard, and whether they had a wide or narrow range. All sets of variable stimuli encompassed the standard. PSE was consistently between the standard and the mean of the variables, as predicted by Adaptation Level Theory. In many experiments, the set of variables is chosen on the basis of theory or pilot studies; the present study shows that PSE will be spuriously drawn toward the center of the variables, hence toward E’s pre-experimental expectations.