Oculomanual Coordination in Tracking of Pseudorandom Target Motion Stimuli

Oculomanual coordination was investigated in 9 healthy subjects during tracking of pseudorandom motion stimuli. Each subject was required to track visual stimuli under eye-hand (EH) and eye-alone (EA) conditions. Subjects were exposed to 3 types of mixed sinusoidal stimulus with varying frequency or amplitude of the highest frequency component, or various degrees of irregularity. Progressive degradation in tracking performance was nonlinearly induced by an increase in either (a) the highest frequency component or (b) its amplitude, but not by stimulus irregularity. No significant difference was found in eye velocity gain and phase under the EH and EA conditions. Eye and hand responses were found to be highly correlated in gain and phase when compared across frequencies and motion stimuli. The results suggest that frequency and amplitude are dominant factors controlling the breakdown of oculomanual performance in response to pseudorandom stimuli. Frequency responses of smooth pursuit eye movements are not affected by the hand motion in pursuit of unpredictable stimuli. Eye and hand motor systems appear to share common nonlinear drive mechanisms when pursuing pseudorandom target motion stimuli.     

Interaction of frequency and magnitude of reinforcement on concurrent performances

Frequency and magnitude of reinforcement were varied in concurrent variable-interval variable-interval schedules of reinforcement. The relative response rate to the two stimuli did not support the notion that choice approximately matches relative total access to food (the product of frequency and magnitude of reinforcement in one schedule divided by the sum of products of frequency and magnitude in both schedules). Relative response rates matched relative reinforcement value when that measure was adjusted to give more emphasis to reinforcement frequency than to reinforcement duration.     

Retrieval of item frequency information in a continuous memory task

The accuracy and response latency of absolute frequency judgments were measured as a function of test lag (the number of intervening items between presentations of a test item) in a continuous memory task. Frequency was varied from one to three presentations in Experiments 1 and 2 and from one to five presentations in Experiment 3. The proportion of correct responses decreased as frequency increased, and correct mean response time tended to increase with frequency. Both accuracy and correct mean response time were found to be largely a function of the most recent test lag. The lag-latency functions were best described by piecewise linear functions, with the breakpoint occurring between lags 1 and 2. Continuous frequency estimation was also shown to improve with extended practice. The implications of the results are discussed with reference to trace strength, numerical-inference, and multiple-trace theories of frequency discrimination.     

Block‐wise conflict adaptation of visual selectivity: Role of hemisphere‐dependent and location‐specific mechanisms

Three experiments investigated views on modulation of visual selectivity that involve hemisphere‐dependence and conflict frequency based views for a whole display. In each experiment, 16 participants completed a flanker task with compatible/incompatible stimulus arrays presented in the left, center, or right visual fields. The relative frequency of the compatible stimulus‐arrays within a trial block was varied as a function of the visual field. In Experiment 1, the relative compatibility frequency in the lateral visual fields was varied (75% / 25%) but not in the center visual field (50%). The results showed that in the lateral visual fields, the performance between the compatible and incompatible trials differed more in conditions with few (vs. many) compatibility trials. Experiments 2 and 3 validated these findings. In Experiment 2, the compatibility frequency varied in the center visual field but not in the lateral fields, resulting in performance effects in all three visual fields. Experiment 3 varied the magnitude of the differences between the compatibility and incompatibility frequencies. Together, the findings showed that participants adjusted to the frequencies of compatible stimuli in all visual fields, indicating conflict adaptation that depends on the relative frequencies of compatible stimuli. The results also suggest that this adaptation is associated with hemisphere‐dependent and location‐specific mechanisms.     

Divided stimulus control: a replication and a quantitative model

Four pigeons were trained on a conditional discrimination. The conditional stimuli were compounds of pairs of stimuli from two different dimensions, fast versus slow cycles of red or green stimuli, and short- versus long-duration presentations of these cycles. Across conditions, the probability of reinforcers for correctly responding to each dimension was varied from 0 to 1. Discriminability, measured by log d, for stimuli on a dimension increased as the relative frequency of reinforcers for that dimension increased, replicating the results of Shahan and Podlesnik (2006). Two further conditions showed that discriminability between stimuli on each dimension was unaffected by whether the stimuli on the other dimension varied or were constant. Finally, maximal discriminability was unchanged in a redundant-relevant cues condition in which either of the stimuli comprising a compound signaled the same correct response. Davison and Nevin's (1999) model provided an excellent quantitative account of the effect of relative reinforcer frequency on discriminability, and thus of the way in which divided stimulus control is itself controlled by relative reinforcement.     

Compounding of pre-aversive stimuli

When two discriminative stimuli, each capable of maintaining a response, are combined, their compound will maintain a frequency of response greater than the frequencies maintained by the individual stimuli. This has been called additive summation. The present experiments extended the investigation of this phenomenon to a converse situation in which two pre-aversive stimuli were combined. Each pre-aversive stimulus was capable of reducing the frequency of an ongoing response. The combination of these stimuli reduced the relative frequency of response below that resulting from either stimulus. Furthermore, the compounding of two highly suppressive stimuli produced more suppression than the compounding of two less-suppressive stimuli. Evidence was also presented to suggest that the compound continued to reduce responding even when the single stimuli were no longer effective. A fourth experiment demonstrated that summation of response tendencies could not be accounted for in terms of stimulus intensity or sensory interaction.     

Choice between response units: The rate constancy model

In a conjoint schedule, reinforcement is available simultaneously on two or more schedules for the same response. The present experiments provided food for key pecking on both a random-interval and a differential-reinforcement-of-low-rate (DRL) schedule. Experiment 1 involved ordinary DRL schedules; Experiment 2 added an external stimulus to indicate when the required interresponse time had elapsed. In both experiments, the potential reinforcer frequency from each component was varied by means of a second-order fixed-ratio schedule, and the DRL time parameter was changed as well. Response rates were described by a model stating that time allocation to each component matches the relative frequency of reinforcement for that component. When spending time in a given component, the subject is assumed to respond at the rate characteristic of baseline performance. This model appeared preferable to the absolute-rate version of the matching law. The model was shown to be applicable to multiple-response concurrent schedules as well as to conjoint schedules, and it described some of the necessary conditions for response matching, undermatching, and bias. In addition, the pigeons did not optimize reinforcer frequency.     

Frequency analysis of electromyographically measured covert speech behavior

Eleven subjects were asked to silently read slides of the letters “P” and “T,” and to view meaningless control slides similarly as they were presented visually. One-eighth-second electromyographic excerpts were sampled from the baseline and response periods. The data were then transformed into the frequency domain for inferential analyses. The mean power spectral frequencies for the response period were significantly lower than those for the base-line in the overall analysis. There were, however, no significant changes from baseline as a function of kind of stimulus (T, P, or Control) or muscle activated (lips or tongue). It was concluded that there was a generalized responding, not unique to the processing of the specific stimuli studied. Frequency analysis of EMG measures of covert behavior holds some promise of yielding unique information not available through traditional analysis procedures, but more sensitive methods than those used here would be required to demonstrate this.     

The N2 in go/no-go tasks reflects conflict monitoring not response inhibition

The functional significance of the N2 in go/no-go tasks was investigated by comparing electrophysiological data obtained from two tasks: a go/no-go task involving both response inhibition as well as response conflict monitoring, and a go/GO task associated with conflict monitoring only. No response was required to no-go stimuli, and a response with maximal force to GO stimuli. The relative frequency of the go stimuli (80% vs. 50%) was varied. The N2 peaked on both no-go and GO trials, with larger amplitudes for both signals when presented in a context of frequent (80%) go signals. These results support the idea that the N2 reflects conflict monitoring not response inhibition.     

Rapid acquisition of bias in signal detection: dynamics of effective reinforcement allocation

We investigated changes in bias (preference for one response alternative) in signal detection when relative reinforcer frequency for correct responses varied across sessions. In Experiment 1, 4 rats responded in a two-stimulus, two-response identification procedure employing temporal stimuli (short vs. long houselight presentations). Relative reinforcer frequency varied according to a 31-step pseudorandom binary sequence and stimulus duration difference varied over two values across conditions. In Experiment 2, 3 rats responded in a five-stimulus, two-response classification procedure employing temporal stimuli. Relative reinforcer frequency was varied according to a 36-step pseudorandom ternary sequence. Results of both experiments were analyzed according to a behavioral model of detection. The model was extended to incorporate the effects of current and previous session reinforcer frequency ratios on current-session performance. Similar to findings with concurrent schedules, effects on bias of relative reinforcer frequency were highest for the current session. However, carryover from reinforcer ratios of previous sessions was evident. Generally, the results indicate that bias can come under control of frequent changes in relative reinforcer frequency in both identification and classification procedures.     

Acquiring conjunctive concepts: When and why does feature frequency affect feature identification?

According to frequency theories of concept attainment, acquisition of rule-governed concepts depends on discriminating relevant from irrelevant stimulus features on the basis of their respective frequencies of occurrence. Depending on the theorist, the critical frequency counts may be based on occurrence in all stimuli or on occurrence in positive instances only. Experiment 1 held frequency in positive instances constant and varied the frequency of irrelevant features in the negative category. High frequency was associated with impaired performance, but only when concept problems started with a negative instance. Experiment 2 demonstrated that some previous findings in the literature that were thought to support frequency theory also depended on problems starting with a negative instance. These findings are not easily reconciled with existing frequency theories. We attribute our results to high intercategory similarity, which is a correlate of high frequency of irrelevant features. In the context of a hypothesis-testing theory, we propose that a negative start stimulus proactively interferes with memory for information in the initial positive instance and that the extent of the interference depends on how similar negative instances are to positive instances.     

The effect of increased response requirements on discriminative performance of the domestic hen in a visual acuity task.

Six domestic hens were trained in a spatial discrimination task. A controlled reinforcement procedure insured that the ratio of scheduled and obtained reinforcement remained equal. Gray stimuli and gratings ranging in spatial frequency from 1 to 10 cycles per millimeter were presented in seven descending series of probes. The response requirement to the sample key was varied from fixed ratio 1 to fixed ratio 40 in seven experimental conditions. An increase in response requirements from fixed ratio 1 to fixed ratio 5 and fixed ratio 10 resulted in significantly higher accuracy at discriminable grating values. Further increases in response requirements did not consistently improve performance. Generally, response biases increased and occasionally became extreme for probes at finer gratings with increased response requirements.     

The effects of varying the distribution of generalization stimuli within a constant range upon the bisection of a sound-intensity interval by rats

Two male, albino rats were trained on a two-valued, self-paced, discrete-trials auditory discrimination. In the presence of a high-intensity stimulus (90 decibels SPL, 4 kiloHertz), response A was reinforced; in the presence of a low-intensity stimulus (50 decibels SPL, 4 kiloHertz), response B was reinforced. When discrimination performance was asymptotic, stimuli intermediate in intensity were presented with the training stimuli in a maintained generalization paradigm. Generalization gradients were derived from the relative frequencies of response A in the presence of each stimulus. A relative frequency of 0.50 was then determined and used as the bisection point of the intensity interval defined by the 90- and 50-decibel stimuli. The bisection point varied with the distribution of the stimuli presented in generalization. This effect was similar to context effects seen in human psychophysics.     

The automatic and the expected self: separating self- and familiarity biases effects by manipulating stimulus probability

Attentional control over prepotent responses has previously been shown by manipulating the probability with which stimuli appear. Here, we examined whether prepotent responses to self-associated stimuli can be modulated by their frequency of occurrence. Participants were instructed to associate geometric shapes with the self, their mother, or a stranger before having to judge whether the sequential shape–label pairs matched or mismatched the instruction. The probability of the different shape–label pairs was varied. There was a robust advantage to self-related stimuli in all cases. Reducing the proportion of matched self pairs did not weaken performance with self-related stimuli, whereas reducing the frequency of either matched mother or stranger pairs hurt performance, relative to when the different match trials were equiprobable. In addition, while mother and stranger pairs jointly benefitted when they both occurred frequently, there were benefits only to self pairs when the frequency of self trials increased along with either mother or stranger trials. The results suggest that biases favoring self-related stimuli occur automatically, even when self-related stimuli have a low probability of occurrence, and that expectations to frequent, self-related stimuli operate in a relatively exclusive manner, minimizing biases to high-probability stimuli related to other people. In contrast, biases to high-familiarity stimuli (mother pairs) can be reduced when the items occur infrequently and they do not dominate expectations over other high-frequency stimuli.     

Poor performance on cognitive tasks in depression: Doing too much or not enough?

Depressed people perform poorly on cognitive tasks. It is unclear whether these deficits are due to decreased devotion of task-related resources or to increased attention to non-task-related information. In the present study, we examined the degree to which depressed and healthy adults displayed pupillary motility that varied at the frequency of presented stimuli on a cognitive task, which we interpreted as task-related processing, and at other frequencies, which we interpreted as reflecting intrinsic processing. Depressed participants made more consecutive errors than did controls. More pupillary motility at other frequencies was associated with poorer performance, whereas more pupillary motility at the frequency of presented stimuli was associated with better performance. Depressed participants had more pupillary motility at other frequencies, which partially mediated observed deficits in cognitive performance. These findings support the hypothesis that allocating cognitive resources to intrinsic processing contributes to observed cognitive deficits in depression.     

The mirror effect in recognition memory

The mirror effect in recognition memory refers to the fact that, with several different classes of stimuli, performance on new items from each class mirrors (is correlated with) performance on the corresponding classes of old items. Classes of stimuli that are accurately recognized as old when old are also accurately recognized as new when new; those that are poorly recognized as old when old are also poorly recognized as new when new. The statement above is shown not to be a tautology. A survey demonstrates that the effect holds for several types of variables (ways to classify stimuli)—word frequency, concreteness, meaningfulness, and others. The survey includes a total of 80 findings. The theoretical implications of the effect are considered.     

Optimal choice

We present a classification and theoretical analysis of discrete-trial and free-operant choice procedures in which reinforcement is assigned to one alternative only, or independently to both, is either always available or conditionally available, and is either "held" or not from trial to trial. Momentary-maximizing and (globally) optimal choice sequences are defined in terms of initializing and marker events. Free-operant choice is analyzed in terms of a clock space whose axes are the times since the last A and B choices. The analysis shows that most molar matching data are derivable from momentary maximizing, and that the momentary-maximizing hypothesis has not been adequately tested in either discrete-trial or free-operant situations.     

Effect of the factor "frequency of words" on temporal and structural characteristics of speech reaction in patients with motor-efferent and motor-afferent aphasia]

The effect of the factor "Frequency of the words" on the speech and the structure of the actualised verbal responses in patients with motor aphasia has been studied. It was established that the rate of the verbal associations occurence depended on the frequency of the word-stimulus and on the probable frequency of the response - stimuli with low frequency prolong the time of the actualisation, especially of the period of sound realisation. Alterations in the psycholinguistic structure of the associative responses were detected - the percentage of the syntagmatic links in both forms of motor aphasia diminished in stimuli with low frequency, which showed that the difficulties in the processes of combination increased. In repeating, reading aloud, writing to dictation with and without pronouncing low frequency words, the number of the mistakes increased and parallel to that the possibilities for their correction decreased. In words with high frequency, reverse correlation to these mentioned above have been established. The results from the study suggested that in preparing the program for the reparative education in patients with motor aphasia, we could rely not only on the "round-about ways" for the reconstruction of the impaired speech system, but also to enlarge considerably the support of its "preserved links". Such a "link" undoubtedly is the considerably preserved speech content of high frequency words.     

Task switching: on the origin of response congruency effects

When people frequently alternate between simple cognitive tasks, performance on stimuli which are assigned the same response in both tasks is typically faster and more accurate than on stimuli which require different responses for both tasks, thus indicating stimulus processing according to the stimulus-response (S-R) rules of the currently irrelevant task. It is currently under debate whether such response congruency effects are mediated by the activation of an abstract representation of the irrelevant task in working memory or by "direct" associations between specific stimuli and responses. We contrasted these views by manipulating concurrent memory load (Experiment 1) and the frequency of specific S-R associations (Experiment 2). While between-task response congruency effects were not affected by the amount of concurrent memory load, they were much stronger for stimuli that were processed frequently in the context of a competitor task. These findings are consistent with the idea that a large portion of the congruency effects stems from direct S-R associations and they do not support a sole mediation by task-set activation in working memory.     

A theory of attending and reinforcement in conditional discriminations

A model of conditional discrimination performance (Davison & Nevin, 1999) is combined with the notion that unmeasured attending to the sample and comparison stimuli, in the steady state and during disruption, depends on reinforcement in the same way as predicted for overt free-operant responding by behavioral momentum theory (Nevin & Grace, 2000). The rate of observing behavior, a measurable accompaniment of attending, is well described by an equation for steady-state responding derived from momentum theory, and the resistance to change of observing conforms to predictions of momentum theory, supporting a key assumption of the model. When probabilities of attending are less than 1.0, the model accounts for some aspects of conditional-discrimination performance that posed problems for the Davison-Nevin model: (a) the effects of differential reinforcement on the allocation of responses to the comparison stimuli and on accuracy in several matching-to-sample and signal-detection tasks where the differences between the stimuli or responses were varied across conditions, (b) the effects of overall reinforcer rate on the asymptotic level and resistance to change of both response rate and accuracy of matching to sample in multiple schedules, and (c) the effects of fixed-ratio reinforcement on accuracy. Some tests and extensions of the model are suggested, and the role of unmeasured events in behavior theory is considered.