What masks utrocular discrimination

Utrocular discrimination, the ability to judge which eye has received monocular stimulation, was studied under conditions designed to reduce the salience of the cue mediating this discrimination. In one series of experiments, these conditions involved reducing the likelihood of motor command signals, overwhelming the motor command centers, and triggering motor command signals for both eyes. Those results indicate that utrocular discrimination is not mediated by ocular movements or command signals. In a second series of experiments, a visual masking paradigrn was used. A monocular test grating appeared superimposed upon a background of binocular masking noise, which was presented either simultaneously with the target or at some interval preceding or following the target (asynchronous masking). When presented simultaneously, the binocular masking noise interfered with utrocular performance, but only when the noise contained spatial frequencies near the test frequency. Masking functions obtained under conditions of asynchronous masking indicated that the time course of the forward and backward masking changed with spatial frequency. Finally, a sustained masking pattern that was ineffective in reducing utrocular performance could be made effective by pulsing the mask simultaneously with the target. Taken together, these results implicate a transient response to the target onset as a critical factor in generating the cue for successful utrocular discrimination. This conclusion may account for the fact that utrocular discrimination falls off for normal observers as the spatial frequency of the target grating increases above 4 cycles/deg.     

Chance results in utrocular discrimination

A review is made of studies on whether we know with which eye we are seeing. The almost total failure to achieve chance results is ascribed to lack of control of convergence and it is shown that such control completely eliminates discrimination.     

On minima of discrimination functions

A discrimination function ψ(x,y) assigns a measure of discriminability to stimulus pairs x,y (e.g., the probability with which they are judged to be different in a same-different judgment scheme). If for every x there is a single y least discriminable from x, then this y is called the point of subjective equality (PSE) for x, and the dependence h(x) of the PSE for x on x is called a PSE function. The PSE function g(y) is defined in a symmetrically opposite way. If the graphs of the two PSE functions coincide (i.e., g≡h⁻¹), the function is said to satisfy the Regular Minimality law. The minimum level functions are restrictions of ψ to the graphs of the PSE functions. The conjunction of two characteristics of ψ, (1) whether it complies with Regular Minimality, and (2) whether the minimum level functions are constant, has consequences for possible models of perceptual discrimination. By a series of simple theorems and counterexamples, we establish set-theoretic, topological, and analytic properties of ψ which allow one to relate to each other these two characteristics of ψ.     

On energy-dependent cues in duration discrimination

We consider the possibility that, in a duration discrimination task involving very short empty time intervals, T and T + ?T, bounded by brief auditory pulses, there may be a critical value of the base duration T within the range 50–300 msec below which duration is coded on the basis of sensory interactions between the markers which bound the interval. With ?T fixed at 10 msec, the functional relation between performance and base duration was determined under three levels of marker intensity. Changing the intensity by 37 dB resulted in the same small change in performance at the shortest base duration (50 msec), where it is most likely that an intensity-dependent interaction could be present, as was obtained at the longest base duration (250 msec), where such an interaction should be minimally effective as a cue for duration discrimination. The code for the duration of an empty auditory interval greater than 50 msee probably is not dorived from energy-dependent processes.     

On the theory of test discrimination

This paper discusses the properties of distributions of test scores and advances the view that the properties of the distribution should depend on the function which the test is intended to perform. A theory of test discrimination is developed which defines discriminatory capacity in terms of the number of relations of difference established by the operation of administering a test ofk items to a sample ofn individuals. A simple proof is presented which indicates that maximum discrimination between individuals is achieved when tests are constructed to yield distributions of the rectangular form. A coefficient of test discrimination is developed. The problem of obtaining in practice distributions approximating to the rectangular form is briefly discussed.This paper was prepared under the auspices of the Defence Research Board, Ottawa, Canada.     

On the use of discrimination to assess memory

A number of studies have made use of sensory discrimination to assess memory. These experiments have typically employed a temporal two-alternative forced choice paradigm in which the interstimulus interval (ISI) is varied. Many of these tests have shown that ISI has little or no effect on discrimination performance. This has been taken as evidence for perfect or very good memory. An alternative interpretation would be that discrimination tests lack sufficient sensitivity to reveal memory effects. In the present study, computer simulations based on signal detection theory were used to estimate the relative effects of memory noise and direct noise (i.e., noise inherent in the discrimination task) on discrimination performance. These simulations indicate that the amount of memory noise has to be quite large to cause a marked elevation in discrimination thresholds and that sensory discrimination is a relatively insensitive test of memory.     

On the failure and facilitation of conditional discrimination.

Pigeons acquired a conditional discrimination in an autoshaping procedure in which certain stimulus combinations (form plus color) were followed by food, whereas others were not followed by food. Although the discrimination normally was acquired quickly, it was completely prevented when the color elements of the stimulus compounds were presented during the intertrial intervals preceding the trials in which both stimulus elements were available. This failure of discrimination was then prevented by having the colors serve as houselights rather than being localized on the response key and by pretraining procedures in which the colors were utilized in simpler discriminations. The results suggest that stimulus salience plays a critical role in determining whether conditional discriminations will be acquired, as the effects of all of the different operations could be understood in terms of increasing or decreasing the salience of the color elements, above or below some threshold value.     

On cross-modal similarity: auditory-visual interactions in speeded discrimination

A series of four experiments explored how cross-modal similarities between sensory attributes in vision and hearing reveal themselves in speeded, two-stimulus discrimination. When subjects responded differentially to stimuli on one modality, speed and accuracy of response were greater on trials accompanied by informationally irrelevant "matching" versus "mismatching" stimuli from the other modality. Cross-modal interactions appeared in (a) responses to dim/bright lights and to dark/light colors accompanied by low-pitched/high-pitched tones; (b) responses to low-pitched/high-pitched tones accompanied by dim/bright lights or by dark/light colors; (c) responses to dim/bright lights, but not to dark/light colors, accompanied by soft/loud sounds; and (d) responses to rounded/sharp forms accompanied by low-pitched/high-pitched tones. These results concur with findings on cross-modal perception, synesthesia, and synesthetic metaphor, which reveal similarities between pitch and brightness, pitch and lightness, loudness and brightness, and pitch and form. The cross-modal interactions in response speed and accuracy may take place at a sensory/perceptual level of processing or after sensory stimuli are encoded semantically.     

On the nature of non-responding in discrimination learning with and without errors

In human subjects, discrimination learning with errors results in active responding incompatible with the reinforced response. The direction of such incompatible behavior is opposite to that of the reinforced response. Responding occurs only during the stimulus correlated with extinction. The frequency of active non-responding is maximal shortly after the start of discrimination training (the time at which the frequency of errors decreases most rapidly) and approaches zero as discrimination training continues. The magnitude of behavioral contrast is not related systematically to the number of errors. Instead it is related directly to the frequency of active non-responding. Active non-responding appears to be motivated by the aversiveness of self-produced frustration, in the sense that active non-responding allows the subject to avoid the aversiveness of non-reinforced responding.     

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.     

Chlordiazepoxide-induced discrimination impairment

Chlordiazepoxide (5.0 and 10.0 mg/kg but not 2.5 mg/kg) administered on 10 successive sessions, significantly impaired the reinforcement-cued discrimination performance of male Sprague-Dawley rats. On three postdrug (saline) recovery sessions, groups previously treated with the drug demonstrated good recovery in discrimination performance. An analysis of response components indicated that the discrimination impairment was due to less inhibition of responding during "no-go" phases of the task by the drugged than control animals. While changes in responding during reinforcement phases may also contribute to the performance of drugged animals, no clear pattern emerges from the present study.     

Vibrotactile frequency discrimination

Thresholds for vibrotactile discrimination of pulse interval were determined for pulse frequencies between 1 and 384 Hz. The results point to a temporal resolution significantly more accurate than that demonstrated in earlier studies. Although touch as a vibratory sensor is in general much inferior to audition, the present results show a striking resemblance to those obtained on auditory pitch. The neurophysiological implications for the tactile as well as for the auditory system are discussed.     

Angular velocity discrimination

Three experiments were designed to investigate naive observers' abilities at discriminating the rotational velocities of two simultaneously viewed objects. In Experiment 1, rotations could occur about parallel or orthogonal axes, with initial orientations in phase or out of phase, and (for parallel rotational axes) in the same or opposite direction. Differential thresholds were approximately 10%. In Experiment 2, stimulus objects differed in the number of faces revealed in rotation (three vs. four). Observers' response curves had no greater spread, but their PSEs (points of subjective equality) were shifted such that there was a partial compensation for faces revealed per unit time. In both Experiment 1 and Experiment 2, performance was consistent across rotational axis and directional conditions. In Experiment 3, the effect of object size was examined, in order to determine the extent to which angular velocity judgments are influenced by the tangential velocity of the faces. When the comparison cube's edges were half the length of the standard's, PSEs were elevated 18.5%. Taken together, these data suggest that observers are able to discriminate angular velocities with a competence near that for linear velocities. However, perceived angular rate is influenced by structural aspects of the stimuli.