Reaction time to the second of two shortly spaced auditory signals both varying in intensity

Six subjects participated in a reaction time (RT) task in which the stimulus events consisted of two sinusoidal waves presented in close succession. The leading stimulus (S₁) had a duration of 25 msec while the binary reaction stimulus (S₂) was 250 msec. Presentation of the interstimulus interval (ISI) was irregular. S₁ as well as S₂ varied in intensity and were assigned randomly the values of 45, 68, 85 and 105 db (SPL). RT to S₂ was examined as a function of the intensity of both stimuli. Generally RT varied inversely with the intensity of S₁ and the downward gradient of RT with ISI became steepened at least for ISIs shorter than 200–250 msec. Concerning S₂, RT grew shorter as the intensity increased up to 85 db. Probably due to startle, RT tended to lengthen at S₂ = 105 db. When both S₁ and S₂ were 105 db the startle effect upon RT seemed most evident. Then the elevation in RT took place at especially those ISIs for which he fastest RTs might have been expected (about 200 msec). For the remaining intensities no interaction between S₁ and S₂ upon RT was found even for the shortest ISIs, implying that the effects of S₁ and S₂ intensities upon RT were independent.     

Perceptual learning in pigeons: Decreased ability to Discriminate samples mapped onto the same comparison in many-to-one matching

Humans often treat two stimuli that are associated with a common response as similar in other contexts. They do so presumably because those stimuli become conceptually or perceptually more similar to each other (perceptual learning). An analogous phenomenon may occur in pigeons when they are trained with a matching-to-sample procedure in which more than one sample is mapped onto the same comparison. In the present research, pigeons were trained to select one comparison following either of two samples (S₁ or S₂) and to select the other comparison following either of two different samples (S₃ or S₄). When the samples were then presented as positive and negative stimuli in a simple successive discrimination, samples that had been associated with the same comparison during original training (e.g., S₁ vs. S₂) were more difficult to discriminate than were samples that had been associated with different comparisons (e.g., S₁ vs. S₃). Thus, it appears that perceptual learning occurs in pigeons as well.     

Slow potential changes and choice reaction time as a function of interstimulus interval

Slow potential changes were recorded over the vertex (C_z) during a choice reaction task. The constant interstimulus interval (ISI) between the visual warning (S₁) and the visual imperative signal (S₂) was either 200, 400, 1000 or 2000 msec. The contingent negative variation (CNV) was not only measured between S₁ and S₂ (CNV₂), but also before S₁ (CNV₁).The main results were: (1) The CNV₂ amplitude showed significant variation as a function of ISI. It reached its maximum with an ISI of 1000 msec. (2) CNV₁ developed only before the short ISIs (200 and 400 msec). (3) When CNV₁ and CNV₂ were summed the differences in CNV amplitudes and durations between different ISIs became smaller. (4) The peak-to-peak amplitude P₁-N₁ of the potential evoked by S₁ was enhanced with short ISIs. (5) The correlations between mean CNV and median reaction time (RT) were low but significant for ISIs of 400, 1000 and 2000 msec. When, however, the effect of subjects was partialized out these correlations were drastically reduced, whereas the partialization of session and block effects had no noticeable influence on these correlations. (6) The correlations between single RT and single CNV (measured for the ISI of 1000 msec, individually for two subjects) were weak or even completely lacking.The main conclusion was that CNV coincides with preparedness to react to a stimulus in a choice RT-task, but its amplitude at the moment of onset of the imperative stimulus does not reflect, or reflects weakly, the degree of preparedness (as indicated by RTs) at that moment.     

Signal recognition models compared for random and Markov presentation sequences

Models of two-category signal recognition are compared to data from a variety of experimental conditions. For recognition, one of two signals (S₁, S₂) which vary slightly on some simple physical dimension is presented on each trial, and 0 is to identify (I₁, I₂ ) which signal was presented. In general, Os show a decrease in both Pr(I₁ /S₂) and Pr(I₂/S₁) for either greater Pr(S₂) or, sequentially, for greater S₂ recency. These effects are described as probability and sequential contrast, respectively. The memory state model (MS) describes a three-state threshold process with responses determined by a simple first-order Markov process which depends on the sensory state and response on the immediately preceding trial. The memory trace regression model (MTR) assumes that O compares the observed signal event with the memory trace of the previous signal event. When the difference is large, the sign of the difference determines the response; when it is small, the response depends on the preceding response. The memory trace is assumed to regress toward the mean signal value. Both models accurately predict the observed bias changes as a function of signal probabilities and of the subsequence of events on the previous trial. The response axioms of the MTR model are modified to predict the results for individual Os for Markov chains of signal events. The response axioms of the MS model are modified to predict responding when information is given to O concerning signal probabilities. Although both models do well under all conditions, the MS model uses fewer parameters and correctly predicts the direction of higher order sequential dependencies.     

Inspection time and response strategies in a choice response task

The effects of varying stimulus duration on two response measures, percentage correct (p_c) and mean reaction time (RT) were investigated in a lights-keys RT task similar to an inspection time (IT) task. One of either N = 2, 4 or 8 lights came on as the stimulus, followed after a range of stimulus exposure durations (D) by all 8, as a backward mask. It was found that p_c was an ogival function of D for all three levels of choice, and that the standard deviations of the best-fitting normal ogives were equal. It is argued that the standard deviation can be taken as a measure of the neural noise, or error-inducing variability introduced by processing the stimulus, and so this result indicated that noise in the choice reaction task is independent of N. The effect of D on RT was as predicted by an optional accumulator model for 7 Ss with RT decreasing as D increased, while another 2 Ss appeared to have adopted a temporal deadline criterion giving RTs independent of D and equal error and correct RTs. The same two response styles were found in a re-analysis of RT data from an IT study. The p_c vs D curves were comparable for both response styles. The accumulator model commonly assumed to underly IT tasks thus does not describe the behaviour of all Ss. Such individual differences in strategic approach to the IT task should be investigated further, since assuming that all Ss use one approach may hide or confound relationships between IT and other measures of individual difference, such as intelligence. Recommendations for better IT measurement techniques are given.     

Successive discrimination training with equated reinforcement frequencies: failure to obtain behavioral contrast

In two experiments, pigeons were trained on two-component multiple schedules in which responding in one component (S₁) was always maintained by a variable-interval schedule. In Experiment I, low response rates were reinforced in the second (S₂) component for six master subjects. This schedule was adjusted to equate reinforcement frequencies in the two components. These subjects were compared to yoked partners, for which reinforcement in the S₂ component was made available on a variable-interval schedule whose value was determined by the master subjects. A similar procedure was used in Experiment II, where the S₂ schedule for master subjects made reinforcers contingent on the absence of responding. No evidence was found in either experiment for a behavioral contrast effect in the S₁ component attributable to response reduction in the S₂ component. A reliable contrast effect was obtained from a group of pigeons given extinction conditions in the S₂ component, which was compared to a group maintained throughout on a multiple variable-interval schedule. The results suggest that previous indications of behavioral contrast in similar situations were probably caused by uneven reinforcement distributions or reflect uncontrolled fluctuations in response rates.     

O2 consumption,heart rate and subjective ratings under conditions of relaxation and active coping

Oxygen consumption, respiratory rate, minute volume, heart rate (HR) and subjective ratings from 12 graduate students were monitored under conditions of relaxation and active coping. The controlled, within-Ss, cross-over design consisted of the two experimental conditions alternating between three control periods. The relaxation condition consisted of an autogenic procedure which the Ss had practiced daily for more than a week. The active-coping condition involved avoidance of an aversive noise during a reaction-time task. In terms of O₂ consumption, there was a slight (3%) but nonsignificant decrease during relaxation. There was a trend for HR to increase during active coping, although this finding was attenuated by the presence of a subset of Ss who responded with a marked and unexpected decrease in HR under this condition. Subjective ratings obtained at 1-min intervals throughout the experiment indicated that the Ss achieved significant levels of subjective relaxation during the procedure. The results of the study failed to support the presence of a hypometabolic state during relaxation as proposed by Benson.     

The effects of single-component extinction of a three-component serial CS on resistance to extinction of the conditioned avoidance response

Central to a fear interpretation of how avoidance responses are maintained in the absence of further CS-UCS pairings is the underlying assumption of an existing gradient of fear across the CS-UCS interval. Extrapolations based on this gradient lead to a number of differential predictions concerning the topography of avoidance responding during extinction. The present research was concerned with the differential effects of extinguishing separate components of the CS complex upon responding to the complete CS complex during extinction. In Phase 1 of the study, rats were classically conditioned to a three-component serial CS (S₁/S₂/S₃) followed by shock. Each subject was then given avoidance training in a one-way apparatus to a criterion of one successful avoidance. In Phase 2, subjects were divided into four groups, with three of the groups receiving nonreinforced exposure for 25 trials to one of the components of the serial CS (S₁, S₂, or S₃). The fourth group (S₀) was exposed for the same period of time to the apparatus cues. In Phase 3, the total stimulus complex was reintroduced in its original order, and animals were tested until extinction of the instrumental response was reached. The results are consistent with the hypothesis that a fear gradient exists in extinction and decreases in magnitude as the distance from the point of UCS onset increases.     

Delayed reinforcement and delayed choice in symbolic matching to sample: Effects on stimulus discriminability

Six pigeons were trained to peck a red side key when the brighter of two white lights (S₁) had been presented on the center key, and to peck a green side key when the dimmer of two white lights (S₂) had been presented on the center key. Equal frequencies of reinforcers were provided for the two types of correct choice. Incorrect choices, red side-key pecks following S₂ presentations and green side-key pecks following S₁ presentations, resulted in blackout. With 0-s delay between choice and reinforcement, the delay between sample presentation and choice was varied from 0 to 20 s. Then, with 0-s delay between sample presentation and choice, the delay between choice and reinforcement was varied from 0 to 20 s. Both types of delay resulted in decreased discriminability (defined in terms of a signal-detection analysis) of the center-key stimuli, but delayed choice had more effect on discriminability than did delayed reinforcement. These data are consistent with the view that the two kinds of delay operate differently. The effect of a sample-choice delay may result from a degradation of the conditional discriminative stimuli during the delay; the effect of a choice-reinforcer delay may result from a decrement in control by differential reinforcement.     

Transcending Lindemann's predictions for the melting temperatures of metals and for the long-wavelength limit of their liquid structure factors

Lindemann's melting criterion remains useful. However, one prediction it makes for liquid metals (our focus here) is that the long-wavelength limit of the structure factor S(q) at freezing, S _{T m} (0), where T _m is the melting temperature, is a universal constant. For 34 metals we have calculated S _{T m} (0) from input data, which is essentially the measured T _m and the surface thickness L, defined near freezing as the product of isothermal compressibility and surface tension. To complete the characterization of S _{T m} (0) we fit to one metal, chosen as Rb, for which S _{T m} (0) is well established experimentally. For a wide variety of metals considered, S _{T m} (0) is then found to vary by a factor of 10.     

A discrete time model for detection of randomly presented stimuli

Considered in this paper is a discrete-time Markov decision process with unobservable states, which occurs in equipment checking, medical diagnosis, signal detection, and reaction time studies. The process is characterized by (i) a state S₀ that at some unknown time t, which is determined probabilistically, turns into an absorbing state S₁; (ii) observations that provide fallible information about the true state and which are taken sequentially to determine whether or not the change from S₀ to S₁ has occurred; and (iii) losses for a false alarm and for delays in detecting the change. A response model is proposed, prescribing a terminal decision as soon as the posterior probability that S₁ obtains reaches or exceeds a fixed probability boundary. Predictions are derived concerning the probability of false alarm and several conditional distributions of the number of observations taken.     

Effect of prior Pavlovian discrimination training upon learning an operant discrimination

The effect of Pavlovian discrimination training with two stimuli upon subsequent learning of an operant discrimination involving those stimuli was studied. After preliminary lever press training, the lever was removed and thirsty rats received noncontingent pairings between S₁ (a tone or a clicker) and water reinforcements, whereas S₂ (a clicker or a tone) occurred always without reinforcement. This procedure presumably established S₁ as a positive CS for respondent behavior, whereas S₂ was established as an inhibitory CS. Following this training, the lever was reintroduced and the rats were trained on an operant (lever pressing) discrimination involving S₁ and S₂. For the Consistent Ss, S₁ was the S^D and S₂ the S^Δ in the operant discrimination; for the Reversed Ss, S₂ served as S^D and S₁ as S^Δ. The Consistent Ss learned the operant discrimination significantly faster than did the Reversed Ss. The result emphasizes the importance of respondents, conditioned to S^D and S^Δ, which modulate operant performance to these stimuli.     

Selective impairment of sensorimotor representations following short-term upper-limb immobilization

In the present experiment, we examined whether short-term upper-limb immobilization would selectively affect the representation of the immobilized limb (using a hand laterality task) or whether the effect of immobilization would extend to another body part (using a foot laterality task). A rigid splint placed on the participants’ left hand was used for immobilization. A control group did not undergo the immobilization procedure. We compared the participants’ performances on the hand and foot laterality tasks before (T₁) and after (T₂) a 48-hour delay, corresponding to the immobilization period. For controls, response time analysis indicated a benefit of task repetition for the recognition of both hand and foot images. For the immobilized group, a slowdown of performance appeared in T₂ for hand images, but not for foot images. The reduced benefit of task repetition following left-hand immobilization appeared for both the immobilized and non-immobilized hand images. These findings revealed that the general cognitive representation of upper-limb movements is affected by the decrease in input/output signal processing due to the left-hand immobilization, while the cognitive representation of lower-limb movements is not.     

Decision and Response in Dual-Task Interference

Experiments with two stimuli (S₁and S₂) and two responses suggest the existence of a stage of processing that cannot be shared between two concurrent tasks. Widespread support has been found for the hypothesis that response selection for Task₂is postponed when the S₁to S₂stimulus onset asynchrony (SOA) is short (Pashler, 1994a). At short SOAs, manipulations which impact Task₂processing prior to response selection (e.g., degradation of stimulus quality) have little effect on Task₂response times (RTs). On the other hand, manipulations which are thought to impact response selection or execution (e.g., Stroop interference) always impact Task₂RTs. There is, however, one particularly compelling demonstration that appears to be inconsistent with the response selection bottleneck hypothesis: Karlin and Kestenbaum (1968) report that the RT difference between detection (i.e., 1-choice) and 2-choice discrimination dramatically decreases with decreasing SOA. Given that the primary difference between detection and discrimination is believed to be at response selection, their result may indicate a processing bottleneck at response execution (Keele, 1973). We fail to replicate the Karlin and Kestenbaum result in two substantive replications of Karlin and Kestenbaum's tasks and procedures. In the single experiment in which Karlin and Kestenbaum's result is replicated, a simple response execution bottleneck account is ruled out by the stability of the difference between 2-choice and 3-choice discrimination times across SOA. Two additional experiments demonstrate that response preparation and task strategy do not substantially contribute to the attenuation of response selection-level effects with decreasing SOA.     

Slow cortical and heart rate correlates of discrimination performance

Slow EEG potentials (F_z, C_z, P_z) and heart rate were recorded during the foreperiod of a reaction task, which involved different levels of discrimination difficulty. A simple reaction task was compared with a selective reaction task where either an easy or a difficult discrimination was required. In general, the terminal amplitude of the CNV was not affected by task difficulty. However, a prolonged negative wave was found when the difficulty of the task was not known to the subject in advance but was indicated by S₁. Moreover, the heart-rate deceleration around S₂ was more pronounced the more difficult the discrimination required at S₂.     

Structural effects on diffusion in metallic glasses: The pressure dependence of Ni diffusion in as-quenched and relaxed Co42Zr58

In order to clarify the role of thermal defects in diffusion in metallic glasses, we have measured the temperature and pressure dependences of diffusion of Ni, a probe for Co, in relaxed and non-relaxed amorphous Co₄₂Zr₅₈ alloys by means of the tracer technique in combination with secondary-ion mass spectroscopy. For the relaxed state, the activation energy and the pre-factor are Q _{= (}1:65=0:08₎ eV and D _{0 =} 2:4+3:9 10-6m2 s-1 respectively. The pressure - 1:9 dependence yields an activation volume V _{act = (}0:66 0:15₎Omega, with Omega being the average atomic volume of the alloy. This value is similar to activation volumes in crystalline materials and is indicative of diffusion via thermally generated defects. Unlike monovacancies in crystals, these defects appear to be spread out, judging from recent isotope-effect measurements. Comparison with literature data shows that the activation volume and hence the diffusion mechanism in metallic glasses clearly depend on the structure and composition even for the very same component. The activation volume in the as-quenched state was found to be _{( )} ^{0:93 0:25 Omega.}     

Refractoriness of on Extended Movement to Directional Change

An extended movement was used to compare the memory-drum and single-channel definitions of psychological refractoriness. The basic movement In response to the first signal (S₁) was a forward lunge and a concurrent arm swing through a target string. The response to the second signal (S₂) was a reversal of the original movement The interstimulus Interval (ISI) ranged from .10 – .70 sec. in .10-sec. steps. The hypothesis that refractoriness of the reversal movement would decrease as ISI shortened was confirmed by the fact that error frequencies decreased significantly and substantially with decreasing IS I. The availability of some residual capacity to deal with S₂ during the refractory period was also indicated by an examination of the relationship between RT₂ and the interval between S₂ and RT₁. This departure from the classical single-channel model shows some agreement with the neuromotor-programming theory.     

One test,five scoring procedures: different ways of approaching the cognitive reflection test

Although the cognitive reflection test (CRT) represents a frequently used instrument within the field of judgement and decision-making, its scope and detailed characteristics are still not well understood. Therefore, the present article discusses 5 different ways of scoring the CRT that include the regular CRT scoring procedure (CRT-Regular), adding up the intuitive answers (CRT-Intuitive), calculating the proportion of intuitive in total incorrect answers (CRT-Proportion Intuitive), scoring only non-intuitive answers irrespective of their correctness (CRT-Reflection) and calculating the proportion of correct in total non-intuitive answers (CRT-Calculation). We conducted 2 studies aimed at investigating the associations among these scoring techniques and their relationships with thinking dispositions, specifically the need for cognition, faith in intuition, superstitious thinking, maximising and post-choice regret. The results indicate that thinking dispositions play a modest role in explaining the performance on the CRT. The specific associations among the investigated dispositions and different CRT scoring techniques are discussed.     

A sensitive rank test for comparing the effects of two treatments on a single group

By taking advantage of an experimental design which increases the number of observations per subject, the sensitivity of the proposed test is increased. In the first of a series of subexperiments, the score of a randomly selected experimentalS is ranked with the scores of the remaining (control)Ss, and the experimentalS is discarded. This procedure is repeated until oneS remains. The test criterion,R _n , is the sum of ranks of the experimentalSs; its exact sampling distribution, a normal approximation, and the sensitivity of the test relative to the WilcoxonT, are described. Because of the large number of scores obtained, the test is particularly useful when preparingSs is more costly than testing them, e.g., in tests following involved conditioning procedures. Since eachS is discarded after experimental treatment, the test fills a real need in studies involving radiation, ablation, or other irreversible treatments.The test criterion, the associated experimental procedure, and the measure of sensitivity are due to SHR; the generating function, tables, and large sample approximation are due to JNC.     

Fatty acid amide hydrolase (FAAH) knockout mice exhibit enhanced acquisition of an aversive, but not of an appetitive, Barnes maze task

It is well established that genetic deletion or pharmacological inhibition of the CB₁ receptor disrupts extinction learning in aversive conditioning tasks, but not in appetitive tasks. Consistent with these findings is that genetic deletion or pharmacological inhibition of fatty acid amide hydrolase (FAAH), the primary catabolic enzyme of the endogenous cannabinoid anandamide (AEA), accelerates acquisition as well as extinction in aversive conditioning tasks. However, it is unknown whether FAAH blockade will affect acquisition in an appetitive conditioning task. Therefore, in the present study, we assessed FAAH (−/−) and (+/+) mice in appetitive and aversive Barnes maze conditioning procedures. Here we report that FAAH (−/−) mice displayed accelerated acquisition rates in an aversively-motivated, but not in the appetitively-motivated, Barnes maze task. The CB₁ receptor antagonist, rimonabant attenuated enhanced acquisition in the aversive procedure, consistent with the idea that elevated AEA levels mediate this apparent nootropic effect. These findings support the hypothesis that stimulation of the endocannabinoid system enhances learned behavior in aversive, but not appetitive, conditioning paradigms.