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.     

Stimulus averaging and the context for judgment

Loudness judgments of stimulus sets composed of four bursts of noise were analyzed for two types of contextual effects: between-set and within-set. Experiment I demonstrated between-set effects for these four-component stimuli; they were shown to be similar to those found in previous work with single stimuli. Experiment 2 tested an averaging model for within-set contextual effects. The results were inconsistent with the model. One interpretation is that there are within-set effects and that these are caused by shifts in the effective range of stimuli. Alternative interpretations attribute the apparent contextual effects either to an averaging of physical values or to an inappropriate scale of judgment.     

Commentary on Wolford,Taylor, and Beck: The conjunction fallacy?

AlthoughP(A&B|X) can never exceedP(A|X) (the conjunction rule), it is possible forP(X|A&B) to exceedP(X|A). Hence, people who rankA&B as more probable thanA are not necessarily violating any normative rule if the ranking is done in terms of the probability of these events to yield an eventX. Wolford, Taylor, and Beck (1990) have argued that this indeed is what happens in some problems (e.g. Tversky& Kahneman’s [1983] Linda problem). The claim made here is that the Linda problem is hard to reconcile with this interpretation; that there is little if any evidence that subjects utilize this interpretation; and that in any case, representativeness can account for all Linda problem results.     

STM capacity for Chinese and English language materials

This paper delineates the theoretical implications of a program of research on short-term memory using Chinese characters as stimuli, and compares the findings with studies of short-term memory that use English language materials. The 14 experiments on which it is principally based, carried out in the People’s Republic of China and in the U.S.A., are reported in detail in Yu et al. (1984), W. Zhanget al. (1984), and G. Zhang and Simon (this issue). One major theoretical product of this research is an experimentally tested model that reconciles the chunking theory of STM capacity with the articulatory loop theory of Baddeley, making good quantitative predictions of capacity compatible with both. Another result, obtained by using homophones as stimuli, is a demonstration that STM is mainly acoustically encoded, but that there are an additional two or three chunks of visually or semantically encoded short-term memory available. Chunks are shown to play the same role in immediate recall and rote learning in both the Chinese language and English language stimuli; and STM capacity, measured in chunks, is essentially the same for materials in both languages.     

The relative accessibility of phonemes and syllables

Previous research comparing detection times for syllables and for phonemes has consistently found that syllables are responded to faster than phonemes. This finding poses theoretical problems for strictly hierarchical models of speech recognition, in which smaller units should be able to be identified faster than larger units. However, inspection of the characteristics of previous experiments’ stimuli reveals that subjects have been able to respond to syllables on the basis of only a partial analysis of the stimulus. In the present experiment, five groups of subjects listened to identical stimulus material. Phoneme and syllable monitoring under standard conditions was compared with monitoring under conditions in which near matches of target and stimulus occurred on no-response trials. In the latter case, when subjects were forced to analyze each stimulus fully, phonemes were detected faster than syllables.     

Orienting responses to pleasant stimuli when expecting pleasant or unpleasant events

The aim was to investigate further the effect of more vigorous orienting to stimuli denoting common fears than to neutral stimuli in subjects threatened with shock. In two experiments, orienting responses (ORs) to pleasant and to neutral words were compared. In Experiment I, the subjects were expecting shock and, in Experiment II, pleasant music. In neither experiment were there differences either in the magnitudes or in the habituation rates of the electrodermal ORs. For clarification, there should be control both of the subjective salience of the stimuli and also of the level of expectation.     

Sinusoidal plucks and bows are not categorically perceived,either

Cutting and Rosner (Perception & Psychophysics, 1974,16, 564–570) reported that two acoustic nonspeech continua varying in rise time were categorically perceived. We have already shown (Rosen & Howell,Perception & Psychophysics, 1981,30, 156–168) that the reason their sawtooth continuum was perceived in such a way, and in particular why it exhibited a midcontinuum peak in the discrimination function, was entirely due to the stimuli not having the intended rise times. The other nonspeech continuum that varied in rise time and was reported to be categorically perceived used a sinusoidal carrier. Although the labeling functions obtained were not as sharp as those obtained with sawtooth stimuli, the characteristic midcontinuum discrimination peak was found. We generated such a set of sinusoidal stimuli and found no evidence of categorical perception. Just as we have previously found for sawtooth stimuli, discrimination is best at the short rise-time end of the continuum and decreases monotonically with increasing rise time.     

A test of independence of dimensions in multidimensional scaling

Models for multidimensional scaling use metric spaces with additive difference metrics. Two important properties of additive difference metrics are decomposability and intradimensional subtractivity. A prediction was derived from these properties and tested experimentally. Rectangles varying in area and shape served as stimuli. Dissimilarity judgments were obtained by both rating and pair comparison procedures. The assumptions of the model were violated by most of the Ss. Apparently this violation was due to an interaction between the two dimensions.     

Transswitching and contextual conditioning

An empirical evaluation of temporal aspects of contextual conditioning was conducted in relation to Asratyan’s (1965) theory of transswitching and to an alternative explanation that was partly stimulated by the Rescorla-Wagner model (Rescorla and Wagner 1972). On the basis of a human electrodermal conditioning preparation suggested by Kimmel and Ray (1978), five groups with 12 subjects each were run. The results indicated that the basic phenomena of transswitching are robust and therefore could be replicated; but the Asratyan theory was rejected. All the results supported an alternative explanation: in contextual conditioning, duration of contextual stimuli is less important than order. Phasic switching is due to simultaneous occurrence of stimuli (differential compound conditioning) and is therefore compatible with the Rescorla-Wagner model. Tonic switching is due to signals that occur before a marked sequence of conditioning trials, in part a challenge to the Rescorla-Wagner model. Long delays between critical events can perhaps be compensated for by mediating memory processes.     

Auditory and phonetic processes in place perception for stops

Use of the selective adaptation procedure with speech stimuli has led to a number of theoretical positions with regard to the level or levels of processing affected by adaptation. Recent experiments (i.e., Sawusch & Jusczyk, 1981) have, however, yielded strong evidence that only auditory coding processes are affected by selective adaptation. In the present experiment, a test series that varied along the phonetic dimension of place of articulation for stops ([da]-[ga]) was used in conjunction with a [ska] syllable that shared the phonetic value of velar with the [ga] end of the test series but had a spectral structure that closely matched a stimulus from the [da] end of the series. As an adaptor, the [ska] and Ida] stimuli produced identical effects, whereas in a paired-comparison procedure, the [ska] produced effects consistent with its phonetic label. These results offer further support for the contention that selective adaptation affects only the auditory coding of speech, whereas the paired-comparison procedure affects only the phonetic coding of speech. On the basis of these results and previous place-adaptation results, a process model of speech perception is described.     

The influence of the interaction of weight and volume on subjective heaviness

A model previously proposed for the size-weight illusion (Cross & Rotkin, 1975) was found unsatisfactory because the postulated volume parameter was not independent of the unit of measurement of weight and the model yielded a paradoxical prediction that the perceived heaviness of small objects should decrease as their weight increased. A new model was proposed based on Stevens and Rubin’s (1970) finding that heaviness functions are a family of con-verging power functions and some of Cross and Rotkin’s developments. The model was ex-amined by estimating its parameters from data previously reported by Cross and Rotkin, Stevens and Rubin, and Kolehmainen and Mikkonen (1970). The equations was found to fit each set of data well. Four independent estimates of a volume parameter of the model were in close agreement, .18, .21, .21, and .24, which is consistent with the model. nt]mis|This research was supported by Grants A0151 and A9582 from the National Research Council of Canada.     

Computation of psychophysical thresholds using the probit technique

Probit analysis is a statistical technique that can be used for the computation of psychophysical thresholds, although it was originally developed for the analysis of pharmacological and toxicological data. Probit analysis may be applied to psychophysical data if the method of constant stimuli has been used for data collection. A computer program written in APPLESOFT BASIC that performs probit analyses on such psychophysical data is presented and explained.     

Plucks and bows are categorically perceived,sometimes

Cutting and Rosner (Perception & Psychophysics, 1974,16, 564–570) reported that sawtooth wavetrains were perceived categorically when an array was varied in linear rise time increments. That is, rapid rise time stimuli were identified as plucked strings and slower rise time stimuli as bowed strings, and pluck-bow comparisons were relatively easy to discriminate but pluck-pluck and bow-bow comparisons were not. Such results indicate the general equivalence of identification and discrimination tasks. Rosen and Howell (Perception & Psychophysics, 1981,30, 156–168), however, report that categorical perception does not occur for these sounds for two reasons. First, the original stimuli did not have the rise times reported by Cutting and Rosner. Second, the perception of these stimuli more closely follows a prediction from a Weber fraction. Acknowledging the first fact to be true, in part due to difficulties in digital-to-analog conversion, I set out to replicate and extend the results of Rosen and Howell. In Experiment 1, I found that stimuli with equal linear increments of rise time are not perceived categorically; but they are not perceived to follow closely a logarithmic relation either. In Experiment 2, I found that stimuli with equal logarithmic increments of rise time were generally perceived categorically. Experiment 3 replicated the results of both experiments. Thus, plucked and bowed music-like sounds can sometimes be found to be perceived in a categorical manner. However, categorical perception is not found with stimuli generated in the manner of Cutting and Rosner (1974) or Rosen and Howell (1981), and the phenomenon generally seems subject to rather stringent, if not curious, stimulus conditions. Moreover, and more deeply, categorical perception seems hardly the bedrock phenomenon it once appeared to be, whether in speech or in any other domain.     

Inverse statistics and misperception of exponential growth

Exponential growth presented by numerical series or graphs is grossly underestimated by human subjects. This misperception was considerably lessened by presenting decreasing functions; this conclusion holds for both numeric and graphic stimuli. In the numerical conditions, about 25% of the subjects performed according to the statistical norm. In contrast with previous results, considerable individual differences with respect to sensitivity for rate of growth were observed. This finding was interpreted in terms of task difficulty: Extrapolation of ascending series is too difficult a task to be discriminative. Extrapolation of descending series is much easier, and may therefore better discriminate among subjects.     

On neurotransmitter mechanisms of reinforcement and internal inhibition

Experiments reported in this study have been performed in order to investigate cholinergic and GABA-ergic neurotransmitter systems and substance P in the realization of internal inhibition and pain reinforcement. This was accomplished during the elaboration of inhibitory and defensive conditioned reflexes to light flashes in alert, nonimmobilized rabbits. Present results together with a review of past research indicate that the cholinergic system is directly involved in transmitting the effects of pain reinforcement to neocortical neurons. Substance P, a neuropeptide, reduces the background activity of neocortical and hippocampol neurons and the response of cortical neurons to pain and positive conditioned stimuli. The cholinergic system and substance P exert a modulating effect on the elaboration of internal inhibition. Phenybut, a GABA derivative capable of penetrating the blood-brain barrier, enhances inhibitory hyperpolarization in the cerebral cortex and improves discrimination between the inhibitory and reinforcing light flashes. It appears, therefore, that the GABA-ergic system plays a leading part in the elaboration of internal inhibition. Neuronal activity and slow potential changes in response to positive conditioned and pain stimuli occur in the same direction after administering the preparations, and the dynamics of these changes is different from that in responses to inhibitory stimuli. It may be supposed on these grounds that the neurotransmitter and neuromodulator systems studied possess a considerable degree of plasticity.     

Combining Item Response Theory and Diagnostic Classification Models: A Psychometric Model for Scaling Ability and Diagnosing Misconceptions

Traditional testing procedures typically utilize unidimensional item response theory (IRT) models to provide a single, continuous estimate of a student’s overall ability. Advances in psychometrics have focused on measuring multiple dimensions of ability to provide more detailed feedback for students, teachers, and other stakeholders. Diagnostic classification models (DCMs) provide multidimensional feedback by using categorical latent variables that represent distinct skills underlying a test that students may or may not have mastered. The Scaling Individuals and Classifying Misconceptions (SICM) model is presented as a combination of a unidimensional IRT model and a DCM where the categorical latent variables represent misconceptions instead of skills. In addition to an estimate of ability along a latent continuum, the SICM model provides multidimensional, diagnostic feedback in the form of statistical estimates of probabilities that students have certain misconceptions. Through an empirical data analysis, we show how this additional feedback can be used by stakeholders to tailor instruction for students’ needs. We also provide results from a simulation study that demonstrate that the SICM MCMC estimation algorithm yields reasonably accurate estimates under large-scale testing conditions.     

An Apple II-based slide-projector laboratory

We describe the software and hardware of a laboratory running under UCSD Pascal on an Apple II computer. The system includes: two random-access projectors and two standard projectors, all equipped with tachistoscopic shutters; two filter wheels; a voice key; a tone generator; and eight response boxes. The laboratory can be used for any experiment in which visual stimuli are to be presented and in which precise display times, reaction times, and luminances are required. It is particularly well suited to picture-perception and picture-memory experiments.     

An IBM XT-compatible,computer-based,slide-projector laboratory

In the present paper, we describe the software and hardware of an on-line, visual-memory laboratory running under Turbo Pascal on an IBM PC XT-compatible computer. The display system includes one Kodak random access projector and four standard Kodak carousel projectors, all equipped with tachistoscopic shutters and luminance-control devices. The response system consists of eight 16-key response boxes. The laboratory can be used for any experiment in which 35-mm slides are to be used as stimuli, and in which precise display times, stimulus luminances, and reaction times are required. The laboratory is particularly well suited to picture-perception and picture-memory experiments.