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Humans can monitor actions and compensate for errors. Analysis of the human event-related brain potentials (ERPs) accompanying errors provides evidence for a neural process whose activity is specifically associated with monitoring and compensating for erroneous behavior. This error-related activity is enhanced when subjects strive for accurate performance but is diminished when response speed is emphasized at the expense of accuracy. The activity is also related to attempts to compensate for the erroneous behavior.

This work examines the manufacture and use of nanocomponents and how they can affect the life cycle impact of resulting nanoproducts. Available data on the production of nanoproducts and nanocomponents are used to identify the major groups of nanocomponents studied in this paper: inorganic nanoparticles, carbon-based nanomaterials, and specialty/composite materials. A comparison of existing results for life cycle assessments of nanocomponents and nanoproducts is used to possibly identifytrends in nanomanufacturing based on material grouping with regard to nonrenewable energy use and greenhouse gas emissions. Continuing work is needed in this area to incorporate other factors such as toxicity and resource consumption in addition to energy use and global warming potential to fully understand the role of nanomanufacturing in the life cycle of nanoproducts.

Using a response-priming procedure, five experiments examined the effects of vowel similarity on the motor programming of spoken syllables. In this procedure, subjects prepared to produce a pair of spoken syllables as rapidly as possible, but sometimes had to produce the syllables in reverse order instead. The spoken responses consisted of consonant-vowel-consonant (CVC) syllables whose medial vowels were /i/, /I/, /λ/, and /α/. Performance was measured as a function of the phonetic relationship between the vowels in a syllable pair. Longer response latencies occurred for syllable pairs that contained similar vowels (e.g., /i/ and /I/) than for syllable pairs that contained dissimilar vowels (e.g., /i/ and /λ/). This inhibitory vowel-similarity effect occurred regardless of whether the initial consonants of the syllables in a pair were the same or different. However, it decreased substantially when the final consonants of the paired syllables were different. These results suggest that a lateral-inhibition mechanism may modulate the motor programming of vowels during speech production. They also provide evidence for the integrity of vowel-consonant (VC) subunits in syllables.

ments that may provide insight into how information from the eyes is actually used. Then we report the results of three experiments designed to answer several questions about the role of eye movements and visual information in the control of limb movements. The answers to these questions have a number of important implications. In particular, they may lead to a better understanding of the mechanisms that mediate aimed limb movements—a type of behavior that most people produce many times each day. The answers may also help to increase our understanding of the relation between the perceptual and motor systems, which serve as the primary interface between people and their environment.

The use of membrane immobilization to carry out the batch dechlorination of trichloroethylene (TCE) using bimetallic Fe/Ni (4:1, Fe to Ni) nanoparticles in cellulose acetate membranes is examined using modeling of transport phenomenon based on experimental results. Membranes are synthesized using both gelation and solvent evaporation techniques for phase inversion. The reduction of metal ions within cellulose acetate phase-inversion membranes was accomplished using sodium borohydride reduction to obtain up to 2 wt % total metals. Characterization of the mixed-matrix structure reveals a bimodal particle distribution ranging between 18 and 80 nm within the membrane cross section. The distribution is the result of changes in the morphology of the cellulose acetate support. The diffusivity and linear partitioning coefficient for the chlorinated organic were measured and are 2.0 x 10(-8) cm2.s-1 and 3.5 x 10(-2) L.g-1, respectively. An unsteady-state model for diffusion through a membrane with reaction was developed to predict experimental results with an error of only 7.2%. The error can be attributed to the lack of the model to account for loss of reactivity through pH effects, alloy effects (bimetallic ratio), and oxidation of nanoparticles. Simulations were run to vary the major transport variables, partitioning and diffusivity, and determine their impact on reaction kinetics. Of the two, diffusivity was less significant because it really only influences the time required for maximum TCE partitioning to the membrane to be achieved and has no effect on the limiting capacity of the membrane for TCE. Therefore, selection of an appropriate support material is crucial for development of highly reactive mixed-matrix membrane systems.

Three experiments were conducted to study motor programs used by expert singers to produce short tonal melodies. Each experiment involved a response-priming procedure in which singers prepared to sing a primary melody but on 50% of trials had to switch and sing a different (secondary) melody instead. In Experiment 1, secondary melodies in the same key as the primary melody were easier to produce than secondary melodies in a different key. Experiment 2 showed that it was the initial note rather than key per se that affected production of secondary melodies. In Experiment 3, secondary melodies involving exact transpositions were easier to sing than secondary melodies with a different contour than the primary melody. Also, switches between the keys of C and G were easier than those between C and E. Taken together, these results suggest that the initial note of a melody may be the most important element in the motor program, that key is represented in a hierarchical form, and that melodic contour is represented as a series of exact semitone offsets.

This is the final report for a project that was a continuation of an earlier, long-term project on the development and validation of the EPIC cognitive architecture for modeling human cognition and performance. The report summarizes the results and lists the products and publications resulting from the project. These including the modeling system software, tutorials, fundamental architecture development, modeling of visual search, and empirical work on working memory and procedure learning.

Although numerous articles have been published documenting parachute injuries, a search of the medical literature revealed none that detail casualty, attrition, and surgery rates for airborne operations conducted into actual combat. This study examines observed airborne casualty, attrition, and surgery rates in U.S. Army Rangers during combat operations in order to identify risk factors attributed to static-line parachute injuries and provide a comparison to estimated attrition rates.Data were recorded on standardized manual casualty cards and tracking forms while treatment was provided during two missions into Afghanistan during Operation Enduring Freedom and two missions into Iraq during Operation Iraqi Freedom, and then consolidated onto an electronic database for further analysis.There were 4 airborne missions totaling 634 jumpers that resulted in 83 injuries sustained by 76 Rangers (12%). Of those, 27 Rangers (4%) were unable to continue the mission and were subsequently evacuated. There were 11 Rangers (2%) who required surgery following evacuation. The overall observed attrition rate differed from the estimated rate (p = 0.04). Although observed attrition rates did not differ from estimations in Afghanistan (p = 0.75), attrition rates in Iraq were greater than estimated rates (p = 0.02) and observed rates in Afghanistan (p = 0.05).Many factors impact casualty, attrition, and injury patterns. Terrain and equipment load were notable associations analyzed in this study.Medical, logistical, and operational personnel can optimize support for airborne forces through improved estimation of casualty, attrition, and surgical rates. Risk factors associated with military parachuting can potentially provide further accuracy in estimating attrition and are recommended for integration into current models.

The phonological-loop model provides a prominent theoretical description of verbal working memory. According to it, serial recall accuracy should be inversely related to the articulatory duration and phonological similarity of verbal items in memorized sequences. Initial tests of these predictions by A. D. Baddeley and colleagues (e.g., A. D. Baddeley, N. Thomson, & M. Buchanan, 1975) appeared to support the phonological-loop model, but subsequent researchers have obtained conflicting data that putatively disconfirm its assumptions. Such conflicts may have stemmed from less than ideal measurements of articulatory duration and phonological similarity. This article discusses these concerns and proposes new theoretically principled methods for measuring articulatory duration and phonological similarity. Two experiments that used these methods in the context of a verbal serial recall task are reported. The results of these experiments confirm and extend the predictions of the phonological-loop model while disarming previous criticisms of it.

A fundamental issue for psychological science concerns the extent to which people can simultaneously perform two perceptual-motor tasks. Some theorists have hypothesized that such dual-task performance is severely and persistently constrained by a central cognitive “bottleneck,” whereas others have hypothesized that skilled procedural decision making and response selection for two or more tasks can proceed at the same time under adaptive executive control. The three experiments reported here support this latter hypothesis. Their results show that after relatively modest amounts of practice, at least some participants achieve virtually perfect time sharing in the dual-task performance of basic choice reaction tasks. The results also show that observed interference between tasks can be modulated by instructions about differential task priorities and personal preferences for daring (concurrent) or cautious (successive) scheduling of tasks. Given this outcome, future research should investigate exactly when and how such sophisticated skills in dual-task performance are acquired.

Direct manipulation involves a large number of interacting psychological mechanisms that make the performance of a given interface hard to predict on intuitive or informal grounds. This paper applies cognitive modeling to explain the subtle effects produced by using a keypad versus a touchscreen in a performance-critical laboratory task.

Computational modeling of human perceptual-motor and cognitive performance based on a comprehensive detailed information- processing architecture leads to new insights about the components of working memory. To illustrate how such insights can be achieved a precise production system model that uses verbal working memory for performing a serial memory-span task through a strategic phonological loop has been constructed with the Executive-Process/ Interactive-Control (EPIC) architecture of Kieras and Meyer. The model accounts well for empirical results from representative memory-span studies The success of this account stems from five central features of EPIC that may be compared and contrasted with those of other currently popular alternative theoretical frameworks.

Engineering models of human performance permit some aspects of usability of interface designs to be predicted from an analysis of the task, and thus can replace to some extent expensive user testing data. 5/22/13 4:56 PM Predictive Engineering Models Using the EPIC Architecture for a High-Performance Task Page 2 of 10 http://www.sigchi.org/chi95/proceedings/papers/dek_bdy.htm Human performance in telephone operator tasks was successfully predicted using engineering models constructed in the EPIC (Executive Process-Interactive Control) architecture for human informationprocessing, which is especially suited for modeling multimodal, complex tasks. Several models were constructed on an a priori basis to represent different hypotheses about how users coordinate their activities to produce rapid task performance. All of the models predicted the total task time with useful accuracy, and clarified some important properties of the task.

Perceptual-motor and cognitive processes whereby people perform multiple concurrent tasks have been studied through an overlapping-tasks procedure. During this procedure, two successive choice-region tasks are performed with a variable interval (stimulus onset asynchrony, or SOA) between the beginning of the first and second tasks. Subjects' reaction times (RTs) for Task 2 are typically greater after very short SOAs. The RT increase, called the psychological refractory-period (PRP) effect, reveals basic characteristics of multiple-task performance. In the present report, quantitative computational models are formulated to explain and predict the PRP effect together with other related phenomena on the basis of the EPIC information-processing architecture, a theoretical framework for precisely modeling human performance under representative single-task and multiple-task conditions (Kieras & Meyer, 1994, Tech. Report TR-94/ONR-EPIC-1). Computer simulations with these models suggest that the PRP effect may stem from subjects' task strategies and limitations on their peripheral perceptual-motor resources, rather than from a cognitive decision or response-selection 'bottleneck.' The goodness-of-fit between simulated and empirical data documents the EPIC architecture's utility for understanding and characterizing human multiple-task performance.

This research examines how people make movements with pointing devices during human-computer interaction. It specifically concerns the perceptual-motor processes that mediate the speed and accuracy of cursor positioning with electromechanical mice. In three experiments we investigated the spatial and temporal characteristics of positioning movements made with a mouse, analyzing subjects' speed and accuracy as a function of the types of targets that the movements had to reach. Experiment 1 required rapid and accurate horizontal movements to targets that were vertical ribbons located at various distances from the mouse's starting location. The targets for Experiments 2 and 3, respectively, were vertical lines having various heights and rectangular boxes having various heights and widths. Constraints on movement distance along the primary (that is, horizontal) line of motion had the greatest effects on total positioning times. However, constraints on movement distance along a secondary (vertical) line of motion also affected total positioning times significantly. These effects may be localized in different phases of movement (e.g., movement execution and verification). The duration of movement execution (i.e., physical motion) depends primarily on the target distance, whereas the duration of movement verification (i.e., check for endpoint accuracy) depends primarily on target height and width. A useful account of movement execution is provided by stochastic optimized-sub movement models, which have significant implications for designing mice and menu-driven displays.

Mixture distributions are formed from a weighted linear combination of 2 or more underlying basis distributions [g(x) = sigma j alpha j fj(x); sigma alpha j = 1]. They arise frequently in stochastic models of perception, cognition, and action in which a finite number of discrete internal states are entered probabilistically over a series of trials. This article reviews various distributional properties that have been examined to test for the presence of mixture distributions. A new multinomial maximum likelihood mixture (MMLM) analysis is discussed for estimating the mixing probabilities alpha j and the basis distributions fj(x) of a hypothesized mixture distribution. The analysis also generates a maximum likelihood goodness-of-fit statistic for testing various mixture hypotheses. Stochastic computer simulations characterize the statistical power of such tests under representative conditions. Two empirical studies of mental processes hypothesized to involve mixture distributions are summarized to illustrate applications of the MMLM analysis.

The complexity of a movement is known to affect the time it takes to initiate the movement. This effect is thought to reflect changes in the duration of processes that operate on a motor program. This question addressed here is whether programming a movement compels the start of its overt execution. If it does, then the programming processes may be said to occur after the "point of no return." We report results from an empirical procedure and a theoretical analysis designed to study processes before and after this point separately. According to our results, changes in the complexity of a movement affect only the prior set of processes. From this we argue that motor programming does not necessitate response execution and that the point of no return occurs very late in the information-processing system. Language: en

SymmetryApp provides three-dimensional molecular representations from a simple Cartesian coordinate file and carries out user-selected symmetry operations that yield a second image of the molecule. If the specified symmetry is indeed present, this image is identical to the original.

Lors de la periode historique et pendant la periode precedant les contacts, les populations aborigenes de la vallee du fleuve Saskatchewan ont forme plusieurs bandes regionales. Les membres de chaque bande se rassemblaient une fois par an au printemps et parfois en automne. Connus par les Europeens sous le nom de « rendez-vous », ces assemblees etaient des jours et des semaines d'interaction sociale, autour d'une serie de ceremonies religieuses. A partir de preuves archeologiques et historiques six centres de rassemblement ont ete identifies. Les commercants de fourrure ont reconnu l'importance de ces centres. La majorite des postes de commerce des 18 eme et 19 eme siecles fut construite dans ces centres ou entre eux, aux frontieres des bandes regionales. A la fin du 19 eme siecle des reserves furent etablies dans plusieurs de ces centres qui continuent d'etre d'importants sites d'habitation aujourd'hui

Although people experience little difficulty in recognizing printed words and comprehending sentences, they cannot do it instantaneously. Experimental psychologists have recently measured the speed of these mental processes by applying a reaction-time method. The method provides new data concerning the organization and retrieval of familiar semantic information in human memory. It has been found that close relations between the meanings of words help people to recognize and pronounce the words faster, especially when the words are hard to see because of visual distortions. Close relations between word meanings also facilitate the comprehension of some sentences, as indicated by how long a person takes to decide whether the sentences are true or false. The facilitation is not universal, however. When the relation between the meanings of two words must be analyzed carefully, their proximity may actually inhibit mental processing. These results, along with additional findings, support the hypothesis that human memory includes a semantic network that represents various categories of objects at distinct locations linked to specify their relations with each other. The memory structure probably influences a number of different mental processes that use it. One possible access route to the network is through a set of detectors designed to accumulate sensory information and signal the presence of particular words. There also appear to be processes for searching and comparing pieces of knowledge after a person finds the memory locations of designated categories. Further research using the reaction-time method may provide a more detailed inventory of what facts are retrieved directly from memory and what are computed from other stored information (36).

A linear speed-accuracy trade-off has been found for rapid, precisely timed movements from a home position toward a target point. In this trade-off, We = K1 + K2(D/T), where D is the distance between the home position and the target, T is a pre-specified movement time, and We is the standard deviation of the distances actually moved. This result differs from Fitts' law, the commonly observed logarithmic trade-off in aimed movements. A new experiment with wrist rotations was performed to determine what conditions induce the linear trade-off rather than Fitts' law. Three types of condition are considered: movement brevity, feedback deprivation, and temporal precision. The experiment yielded a linear trade-off for precisely timed movements even when their durations significantly exceeded an amount of time (200 ms) sufficient to process visual feedback. This result suggests that the linearity does not depend on movement brevity and/or feedback deprivation per se. Instead it supports a temporal-precision hypothesis that the linear trade-off occurs when aimed movements must have precisely specified durations.

Spreading-activation models for the structure of semantic and episodic memory postulate a network of interconnected nodes in which activation spreads from a source node to recipient nodes. These models account for a broad range of memory-related processes, including word recognition, sentence verification, prose comprehension, and sentence production. A fundamental question regarding this account concerns the nature of activation growth at each node in the network. Two mutually exclusive possibilities are (a) that activation grows in a discrete fashion, making abrupt transitions between two or more distinct states and (b) that activation grows continuously from a resting level to an asymptotic level. In the present article, we characterize this dichotomy with examples from the literature, and we apply an adaptive priming procedure for testing discrete versus continuous activation models. Our procedure involves the presentation of prime stimuli at various moments before a test stimulus; subjects are required to make a lexical (word/nonword) decision about the test stimulus. The duration of the interval between the prime and test stimuli is varied adaptively on the basis of subjects' performance. Reaction times are recorded as a function of this duration. According to discrete activation models, there is a unique reaction-time distribution associated with each possible state of node activation. The distribution of reaction times observed when the test stimulus appears near the moment of transition between discrete states should therefore constitute a finite mixture of the underlying basis distributions associated with the individual discrete activation states. The mixture proportion will depend on the relation between the priming interval and the distribution of state-transition times. Continuous activation models assert instead that activation grows continuously over time and that there is a unique reaction-time distribution associated with any given degree of intermediate priming. Such models predict that no finite mixture distribution will emerge when the priming interval has a fixed intermediate duration. Two experiments with the adaptive priming procedure are reported to test these alternative predictions. In Experiment 1, the prime and test stimuli were semantically associated words (e.g., bread-butter). In Experiment 2, episodic associations between the prime and test stimuli were established through paired associate learning. For both cases, the mixture prediction failed, and two-state discrete activation models were rejected.(ABSTRACT TRUNCATED AT 400 WORDS)

Serial-order information for speech production may be characterized in terms of three alternative classes of models: element-to-element coding. element-to-position coding. and hierarchical coding. Three experiments were conducted to test canonical versions of these models as accounts of the representation of syllable order in short utterances. A response priming procedure was used in which subjects prepared to say a “primary” utterance containing four syllables, but sometimes switched and said a “secondary” utterance containing the same syllables in a different order. Performance (reaction time, duration, and error rate] on the secondary utterance was measured as a function of the ordering of its syllables relative to those of the primary utterance. Experiment I supported a hierarchical coding model consisting of a tree with binary branches. In particular, subjects produced the secondary utterances faster when they were compatible with a binary-tree representation of the primary utterances than when they were not. Experiment 2 supported the hierarchical coding model over an element-to-element coding model. and Experiment 3 supported it over an element-to-position model. The binary structure of the hierarchical coding of syllable order may be based in the rhythmic patterns of speech.

Services developed by the pharmacy department at Walter Reed Army Medical Center (WRAMC) relating to the treatment and study of patients infected with the human immunodeficiency virus (HIV) are described. The WRAMC pharmacy department closely monitored use of azidothymidine (renamed zidovudine) before and after its approval by FDA. It has also done pharmaceutical cost studies for HIV-infected patients by disease stage according to the Walter Reed Classification System. An Army pharmacist at the U.S. Army Centralized Allergen Extract Laboratory is involved with the development and distribution of delayed hypersensitivity skin tests used to determine the progression of the disease; the current test battery correlates with the CD4 T-lymphocyte count, low numbers of which indicate disease progression. The Walter Reed Retrovirus Research Group includes an Army pharmacist who not only is involved with the traditional distributive and clinical aspects of the position but also is involved in clinical pharmacy, pharmacoepidemiology, and social and behavioral research. This pharmacist is the principal investigator on protocols studying the relationship of various factors to the frequency and distribution of both beneficial and adverse pharmaceutical outcomes in this patient population. The pharmacy department at WRAMC has taken an active role in both the treatment of HIV-infected patients and HIV-associated research, as part of an aggressive overall Army effort to develop effective treatment and chemoprophylaxis or immunoprophylaxis for this disease.

Two experiments were conducted with a hybrid procedure that involved a battery of indirect criterion tests designed to study the activation and metacognition of inaccessible stored information. In each experiment, subjects first attempted to recall some rare target words in response to a series of deflnitions meant to tue retrieval from long.term semantic memory. For the words that could not be recalled initially, the subjects rated their feelings of knowing. They then performed a lexicaldecision task in which the target words and other control words were presented. Reaction times were measured as a function of the feeling-of-knowing ratings and the length of the interval between the initial exposure to the definitions and the subsequent lexical decisions. Faster decisions occurred for the target words than for the controls, especially when strong feelings of knowing had been expressed about the tarsets. Similar facilitation was obtained in a subsequent old-new recognition task. It appears that unsuccessful attempts to retrieve inaccessible stored information prime the later recognition of the information through a process of spreading activation. Such activation may sensitize people to future occurrences of stimulus inputs needed for insightful solutions of semantically rich problems.

Some alternative hypotheses about the recognition of ambiguous words are considered. According to the selective-access hypothesis, prior semantic context biases people to access one meaning of an ambiguous word rather than another in lexical memory during recognition. In contrast, the nonselectiveaccess hypothesis states that all meanings of the word are accessed regardless of the context. We tested certain versions of these hypotheses by having students decide whether selected strings of letters were English words. The stimuli included test sequnces of three words in which the second word had two distinct possible meanings, whereas the first and third words were related to these meanings in various ways. When the first and third words were related to the same meaning of the ambiguous second word (e.g., SAVE-BANK-MONEY), the reaction time to recognize the third word decreased. But when the first and third words were related to different meanings of the second word (e.g., RIVER-BANK-MONEY), the reaction time for the third word was not reliably different from a control sequence with unrelated words. These and other data favor the selective-access hypothesis. Selective access to lexical memory is discussed in relation to models of word recognition.

Some reaction time experiments are reported on the relation between the perception and production of phonetic features in speech. Subjects had to produce spoken consonant-vowel syllables rapidly in response to other consonant-vowel stimulus syllables. The stimulus syllables were presented auditorily in one condition and visually in another. Reaction time was measured as a function of the phonetic features shared by the consonants of the stimulus and response syllables. Responses to auditory stimulus syllables were faster when the response syllables started with consonants that had the same voicing feature as those of the stimulus syllables. A shared place-of-articulation feature did not affect the speed of responses to auditory stimulus syllables, even though the place feature was highly salient. For visual stimulus syllables, performance was independent of whether the consonants of the response syllables had the same voicing, same place of articulation, or no shared features. This pattern of results occurred in cases where the syllables contained stop consonants and where they contained fricatives. It held for natural auditory stimuli as well as artificially synthesized ones. The overall data reveal a close relation between the perception and production of voicing features in speech. It does not appear that such a relation exists between perceiving and producing places of articulation. The experiments are relevant to the motor theory of speech perception and to other models of perceptual-motor interactions. Language: en

Three experiments are reported on the role of phonetic features in motor programs for speech production. Each experiment involved a type of response-priming procedure. The procedure required subjects to prepare a specified primary vocal response that contained one or two vowel-consonant syllables (e.g., “up,” “ub,” “ut,” and “ud”). After the preparation interval, the subjects either produced the primary response upon command or else switched to produce another specified secondary response instead. Response latency and accuracy were measured as a function of the relationship between the phonetic features of the primary and secondary responses. Longer latencies and more errors occurred when the secondary response had place-of-articulation or voicing features identical to those of the primary response. The results may be interpreted in terms of an interactive-activation model. It appears that phonetic features play a significant role during the compilation of articulatory motor programs, and that preparation to produce an utterance inhibits the programming of other utterances with similar features. This outcome complements and extends conclusions derived from analyzing naturalistic slips of the tongue and coarticulation phenomena. The interactive-activation model of speech production provides a link with theoretical accounts of speech perception, word recognition, and manual movement.

A stochastic optimized-submovement model is proposed for Pitts' law, the classic logarithmic tradeoff between the duration and spatial precision of rapid aimed movements. According to the model, an aimed movement toward a specified target region involves a primary submovement and an optional secondary corrective submovement. The submovements are assumed to be programmed such that they minimize average total movement time while maintaining a high frequency of target hits. The programming process achieves this minimization by optimally adjusting the average magnitudes and durations of noisy neuromotor force pulses used to generate the submovements. Numerous results from the literature on human motor performance may be explained in these terms. Two new experiments on rapid wrist rotations yield additional support for the stochastic optimizedsubmovement model. Experiment 1 revealed that the mean durations of primary submovements and of secondary submovements, not just average total movement times, conform to a square-root approximation of Pitts' law derived from the model. Also, the spatial endpoints of primary submovements have standard deviations that increase linearly with average primary-submovement velocity, and the average primary-submovement velocity influences the relative frequencies of secondary submovements, as predicted by the model. During Experiment 2, these results were replicated and extended under conditions in which subjects made movements without concurrent visual feedback. This replication suggests that submovement optimization may be a pervasive property of movement production. The present conceptual framework provides insights into principles of motor performance, and it links the study of physical action to research on sensation, perception, and cognition, where psychologists have been concerned for some time about the degree to which mental processes incorporate rational and normative rules. An enduring issue in the study of the human mind concerns of mathematical probability theory and statistical decision thethe rationality and optimality of the mental processes that guide ory (e.g., see Edwards, 1961; Edwards, Lindman, & Savage

Cognitive psychologists have characterized the temporal properties of human information processing in terms of discrete and continuous models. Discrete models postulate that component mental processes transmit a finite number of intermittent outputs (quanta) of information over time, whereas continuous models postulate that information is transmitted in a gradual fashion. These postulates may be tested by using an adaptive response-priming procedure and analysis of reaction-time mixture distributions. Three experiments based on this procedure and analysis are reported. The experiments involved varying the temporal interval between the onsets of a prime stimulus and a subsequent test stimulus to which a response had to be made. Reaction time was measured as a function of the duration of the priming interval and the type of prime stimulus. Discrete models predict that manipulations of the priming interval should yield a family of reaction-time mixture distributions formed from a finite number of underlying basis distributions, corresponding to distinct preparatory states. Continuous models make a different prediction. Goodness-of-fit tests between these predictions and the data supported either the discrete or the continuous models, depending on the nature of the stimuli and responses being used. When there were only two alternative responses and the stimulus-response mapping was a compatible one, discrete models with two or three states of preparation fit the results best. For larger response sets with an incompatible stimulus-response mapping, a continuous model fit some of the data better. These results are relevant to the interpretation of reaction-time data in a variety of contexts and to the analysis of speed-accuracy trade-offs in mental processes.

It is hypothesized that an individual has a preferred unidimensional risk level in a coin-tossing game, and that his preferences are single-peaked over the risk scale. Risk was varied by increasing both the monetary denomination (D = le to $1) and number of tosses (N = 1 to 20) involved in a game. The rank order preference data of 30 subjects within sets of games having either constant D or N, single stimulus preference data, and pair comparison preferences between games supported these hypotheses. Data also supported the existence of a function R,[(D, N)] which maps games onto the risk scale and is monotone increasing in both arguments. However, the exact form of the function may vary, depending on the particular set of games from which the subject chooses. The prevailing expectation theories of individual decision making in a risky situation (Edwards, 1954, 1955) all avoid the subjective variable of riskiness. However, this variable has been given some attention as a stimulus dimension relevant to choice (Coombs and Pruitt, 1960; Royden, Suppes, and Walsh, 1959). In these experimental studies, the variance or some other parameter of the frequency distribution of a game’s possible outcomes was explored as a potential correlate of risk. The evidence supports the hypothesis that variance is a strong correlate of risk in simple game situations, but in more complex situations, the concept of risk is elusive and idiosyncratic (Wilcox, 1967). Thus we have chosen to treat the concept of risk as being undefined in a strict sense, although we do assume the existence of a variable which, in addition to expected value, mediates preferences in a consistent manner, can be experimentally manipulated in various ways, and for intuitive reasons might be identified as risk. The present study considers a number of coin-tossing games which vary in two aspects: the coin denomination (D) involved in a single toss, and the number of tosses (N) composing the complete game. As an example, the game (25@,5) represents a game in which 5 quarters are tossed all at once. For each coin landing heads, the game’s owner is paid a quarter by a bank. For each tail, the bank is paid a quarter by the owner.

A method for studying semantic memory is presented. This method involves measuring the reaction time (RT) of true-false decisions about two kinds of logical assertions, “ALL S ARE P” and “SOME S ARE P,” while varying the set relation and sizes of the semantic categories S and P. Decisions about “ALL S ARE P” are faster when S and P are disjoint than when S intersects P. Effects of category size vary with the set relation of S to P. When S and P are disjoint, increasing P-size increases mean RT, but increasing S-size has no effect; when S is a subset of P, decreasing S-size and increasing P-size increases mean RT. These data are used to infer what semantic information is stored in memory and how this information is retrieved. The approach differs from previous ones that invoke rather strong assumptions about the nature of stored semantic information and its retrieval. With a set of relatively minimal assumptions, the present results permit rejection of five plausible one-stage retrieval models. The failure of these models suggests a two-stage model, in which Stages 1 and 2 are used for deciding whether S intersects P and whether S is a P-subset, respectively. Decisions about “SOME S ARE P” support this two-stage model and reveal detailed properties of Stage 1. When S and P are disjoint, these decisions are as fast as decisions about “ALL S ARE P” and are faster when S intersects P. Effects of category size again vary with the set relation of S to P. The data suggest that Stage 1 involves serial self-terminating comparisons of the name “S” to names of categories that intersect P. Differences obtained by subtracting RTs of decisions about “SOME S ARE P” from RTs of decisions about “ALL S ARE P” reveal detailed properties of Stage 2. One of the originally rejected retrieval models accounts for this stage, which seems to involve self-terminating comparisons of P-attributes to S-attributes. It is concluded that at least two kinds of information about semantic categories, names of categories they intersect and representations of their attributes, are stored in memory and do not require “computation.” The data suggest that stored names of intersecting categories are organized in a network based on amount of category-overlap, but that pointers associated with this network are not informative about the exact set relations between categories. Because of this memory organization, it is apparently impossible to search selectively through either the stored names of a category's subsets or supersets. Accessing the attributes of intersecting categories seems to require a prerequisite search of category names. The organization of semantic memory therefore determines both when and what stored information can be retrieved.