ADVANTAGES OF THE SAME-DIFFERENT METHOD OVER THE TRIANGULAR METHOD FOR THE MEASUREMENT OF TASTE DISCRIMINATION

The triangular method, the same-different rating method, and the standard same-different method were each used with 10 tasters to obtain estimates of the discriminability of two concentrations of a colorless beverage. There were no significant differences in d', an index of discriminability, among the three tasks. In the light of this parity, a choice amongst the methods should be driven by practical considerations. When receiver operating characteristics (ROCs) were fitted to the rating data, the model underlying published tables of d' was strongly supported, so that discriminability can be assessed from same-different data either by entering tables or by fitting ROC curves. Same-different methods appear more acceptable to tasters than the triangular method.     

TWO MODELS FOR ESTIMATING THE DISCRIMINABILITY OF FOODS AND BEVERAGES

In order to evaluate the suitability of signal detection theory methods for assessing the discriminability of foods and beverages, the discriminability of two dairy milk products that differed in fat content was measured with two detection-theoretic methods: the single-interval rating method, and the same-different method. The nominal fat contents of the milk products were 0.1 and 1.6%. Measures of discriminability for three observers were derived by fitting receiver operating characteristics (ROCs) based on equal-variance normal models to the ratings of each observer with a procedure that combined jackknifing and maximum-likelihood estimation. The fitted ROCs provided a good fit to the data indicating that the equal-variance models were appropriate for these tasks. The best-fitting estimates of d' obtained for each task were not significantly different, demonstrating that d' is a measure of sensitivity that is largely independent of the task from which it is determined. However, estimates of proportion correct obtained for each task were shown to be significantly different.     

False Approximations of the Approximate Number System?

Prior research suggests that the acuity of the approximate number system (ANS) predicts future mathematical abilities. Modelling the development of the ANS might therefore allow monitoring of children's mathematical skills and instigate educational intervention if necessary. A major problem however, is that our knowledge of the development of the ANS is acquired using fundamentally different paradigms, namely detection in infants versus discrimination in children and adults. Here, we question whether such a comparison is justified, by testing the adult ANS with both a discrimination and a detection task. We show that adults perform markedly better in the discrimination compared to the detection task. Moreover, performance on discrimination but not detection, correlated with performance on mathematics. With a second similar experiment, in which the detection task was replaced by a same-different task, we show that the results of experiment 1 cannot be attributed to differences in chance level. As only task instruction differed, the discrimination and the detection task most likely reflect differences at the decisional level. Future studies intending to model the development of the ANS should therefore rely on data derived from a single paradigm for different age groups. The same-different task appears a viable candidate, due to its applicability across age groups.     

Stimulus-dependent adjustment of reward prediction error in the midbrain

Previous reports have described that neural activities in midbrain dopamine areas are sensitive to unexpected reward delivery and omission. These activities are correlated with reward prediction error in reinforcement learning models, the difference between predicted reward values and the obtained reward outcome. These findings suggest that the reward prediction error signal in the brain updates reward prediction through stimulus-reward experiences. It remains unknown, however, how sensory processing of reward-predicting stimuli contributes to the computation of reward prediction error. To elucidate this issue, we examined the relation between stimulus discriminability of the reward-predicting stimuli and the reward prediction error signal in the brain using functional magnetic resonance imaging (fMRI). Before main experiments, subjects learned an association between the orientation of a perceptually salient (high-contrast) Gabor patch and a juice reward. The subjects were then presented with lower-contrast Gabor patch stimuli to predict a reward. We calculated the correlation between fMRI signals and reward prediction error in two reinforcement learning models: a model including the modulation of reward prediction by stimulus discriminability and a model excluding this modulation. Results showed that fMRI signals in the midbrain are more highly correlated with reward prediction error in the model that includes stimulus discriminability than in the model that excludes stimulus discriminability. No regions showed higher correlation with the model that excludes stimulus discriminability. Moreover, results show that the difference in correlation between the two models was significant from the first session of the experiment, suggesting that the reward computation in the midbrain was modulated based on stimulus discriminability before learning a new contingency between perceptually ambiguous stimuli and a reward. These results suggest that the human reward system can incorporate the level of the stimulus discriminability flexibly into reward computations by modulating previously acquired reward values for a typical stimulus.     

INVESTIGATION OF THE DUAL-PAIR METHOD AS A POSSIBLE ALTERNATIVE TO THE TRIANGLE AND SAME-DIFFERENT TESTS

Previous experiments have shown that the same-different test, because of its more suitable cognitive strategy and lower memory requirements, is a more powerful and sensitive alternative to the triangle and duo-trio tests. This project describes an experiment conducted in order to investigate ways to improve further the performance of the same-different test. Three protocols were compared using orange flavored beverages and 24 judges: the same-different method, the triangle test and the dual-pair paradigm. The latter protocol could improve the same-different's performance by preventing the spontaneous variations of the judges'τ criterion. While no significant differences were detected among the d' values obtained with each procedure, a trend was observed for the same-different and dual-pair test to be slightly more sensitive (higher d' values) than the triangle test. Since the same-different test is statistically more powerful, it is a preferable choice over the triangle, duo-trio and dual-pair tests.     

Biological probability: cognitive processes of generating probabilities of events in biological systems.

This paper analyses relationships between probabilities of events happening in biological systems (or probabilistic disposition of systems) and cognitive properties of biological entities comprising such systems. Two kinds of cognitive properties are identified as relevant to the current problem: the ability to respond differently against different configurations of the environment (discriminability of cognition), and the ability to make an appropriate response to maintain a particular relation with the environment (selectivity of cognition). A basic framework bridging the two features of living systems, probabilistic disposition and the cognitive properties, is presented towards a general theory explaining the process generating probabilities of biological events. In this framework, a deterministic model of a system of entities is developed, in which objects are described as subjects that cognize events (i.e. entities as cognizers). Cognition is used in a wider sense, including not only biotic but also abiotic, and cognizers are conceptually distinguished from the meta-observer who describes the system externally. Based on this perspective, this paper seeks to explicate how events can occur in an uncertain, probabilistic manner, if observed from a cognizer viewpoint, even under a deterministic system. Each cognizer is identified with both the set of states that are actually taken, and its motion function which maps its state uniquely to a successor state depending on the current states of itself and of the rest of cognizers constituting the system. The model analysis reveals that the cognitive properties, discriminability and selectivity, of a cognizer can contribute to determining the probability of an event encountered by the cognizer itself-in particular, discrimination reducing the uncertainty in events occurrence for the cognizer. Biological implication of this result is discussed focusing on the concept of the probability of survival and reproduction.     

VISUAL RESOLUTION IN HUMANS FLUCTUATES OVER THE 24H PERIOD*

The present experiment was designed to assess daily fluctuations of visual discriminability, a function reflecting the resolution power of the visual sensitivity by measure of a differential threshold. Sixteen subjects underwent a visual discrimination threshold task (using the constant method) in a protocol allowing one point every 2h over the 24h period. The results show that the visual discrimination threshold is low in the morning and increases progressively over the day, reaching a first peak at 22:00. During the night, the same pattern occurs, with low threshold levels at the beginning of the night and high levels at the end. This profile is quite different from that of detection threshold variations, suggesting that the two visual functions are under the control of different underlying mechanisms. Two interpretations could account for this discrepancy. The first relates to different oscillators in the eye for detection and discrimination. The second refers to a possible linkage of visual discriminability with the sleep-wake cycle since threshold measures were systematically low (i.e., high resolution power) after long sleep periods. (Chronobiology International, 17(12), 187–195, 2000)     

Time-integrated position error accounts for sensorimotor behavior in time-constrained tasks

Several studies have shown that human motor behavior can be successfully described using optimal control theory, which describes behavior by optimizing the trade-off between the subject's effort and performance. This approach predicts that subjects reach the goal exactly at the final time. However, another strategy might be that subjects try to reach the target position well before the final time to avoid the risk of missing the target. To test this, we have investigated whether minimizing the control effort and maximizing the performance is sufficient to describe human motor behavior in time-constrained motor tasks. In addition to the standard model, we postulate a new model which includes an additional cost criterion which penalizes deviations between the position of the effector and the target throughout the trial, forcing arrival on target before the final time. To investigate which model gives the best fit to the data and to see whether that model is generic, we tested both models in two different tasks where subjects used a joystick to steer a ball on a screen to hit a target (first task) or one of two targets (second task) before a final time. Noise of different amplitudes was superimposed on the ball position to investigate the ability of the models to predict motor behavior for different levels of uncertainty. The results show that a cost function representing only a trade-off between effort and accuracy at the end time is insufficient to describe the observed behavior. The new model correctly predicts that subjects steer the ball to the target position well before the final time is reached, which is in agreement with the observed behavior. This result is consistent for all noise amplitudes and for both tasks.     

Prefrontal neurons predict choices during an auditory same-different task

The detection of stimuli is critical for an animal's survival [1]. However, it is not adaptive for an animal to respond automatically to every stimulus that is present in the environment [2-5]. Given that the prefrontal cortex (PFC) plays a key role in executive function [6-8], we hypothesized that PFC activity should be involved in context-dependent responses to uncommon stimuli. As a test of this hypothesis, monkeys participated in a same-different task, a variant of an oddball task [2]. During this task, a monkey heard multiple presentations of a "reference" stimulus that were followed by a "test" stimulus and reported whether these stimuli were the same or different. While they participated in this task, we recorded from neurons in the ventrolateral prefrontal cortex (vPFC; a cortical area involved in aspects of nonspatial auditory processing [9, 10]). We found that vPFC activity was correlated with the monkeys' choices. This finding demonstrates a direct link between single neurons and behavioral choices in the PFC on a nonspatial auditory task.     

Activation in posterior superior temporal sulcus parallels parameter inducing the percept of animacy

An essential, evolutionarily stable feature of brain function is the detection of animate entities, and one of the main cues to identify them is their movement. We developed a model of a simple interaction between two objects, in which an increase of the correlation between their movements varied the amount of interactivity and animacy observers attributed to them. Functional magnetic resonance imaging revealed that activation in the posterior superior temporal sulcus and gyrus (pSTS/pSTG) increased in relation to the degree of correlated motion between the two objects. This activation increase was not different when subjects performed an explicit or implicit task while observing these interacting objects. These data suggest that the pSTS and pSTG play a role in the automatic identification of animate entities, by responding directly to an objective movement characteristic inducing the percept of animacy, such as the amount of interactivity between two moving objects.     

EMG biofeedback and discriminative muscle control

The awareness model of biofeedback suggests that training teaches new skills or enhances performance at old skills, while the cognitive or feed-forward models suggest that biofeedback brings attention to the response of interest but does not actually increase task skill. In a test of the predictions made by these models, subjects were tested on one or more cross-modal matching tasks, provided brief training, and retested on the task(s). Thirty subjects participated in integer-matching tasks in which they were instructed to produce various levels of frontalis activity corresponding to the levels of a ratio scale. Forty-five subjects participated in a tone-matching task in which they tried to match their frontalis tension to the pitch of a tone. The results indicated that the groups receiving biofeedback training improved at the more difficult integer task and at the tone task. Subjects performed better on the integer tasks than at the tone task. Our findings suggest that an awareness model accounts for changes occurring during biofeedback training. However, an awareness model may be applicable only for tasks of moderate difficulty; for relatively easy tasks, a feed-forward model may be more appropriate. The clinical utility of cross-modal matching tasks is also described.     

朝向和对比度同时快速变化条件下的分辨能力

在自然的视觉中,投射到视网膜上的视觉图像总是在不停地变化,而人类的感知系统依然可以准确高效地识别物体.因此,人类的感知系统有相应的快速处理机制以应对这种动态变化．然而,前人的实验都是在相对稳定的刺激条件下研究人类被试的感知系统对一个刺激参数的反应,比如在固定对比度下测试朝向分辨能力,或在固定朝向测定对比度分辨能力,而朝向和对比度同时变化时,人类对这两个参数的分辨能力仍然缺乏研究．因此,在本实验中,我们使用朝向和对比度同时变化的刺激,研究了人类被试对朝向和对比度的分辨能力．结果表明,在这种动态变化的条件下,被试对朝向和对比度的分辨阈值都有显著性的降低．而且,朝向分辨阈值降低的幅度与在固定对比度参数条件下的分辨阈值成负相关,即在固定对比度条件下朝向分辨阈值较高的被试,在朝向和对比度同时变化条件下,其朝向分辨阈值降低的幅度相对要大,朝向分辨能力也就相对地提高更大．对比度分辨能力也呈现同样的规律．这些结果说明,朝向和对比度的同时变化提高了被试对朝向和对比度的分辨能力,一个参数变化时其分辨能力越低的被试,两个参数变化时其分辨能力提高的幅度就越大．揭示了视觉系统处理这种多刺激参量信息变化的能力和机制,对人类视觉系统在真实的视觉过程中如何处理朝向和对比度信息提供了认识．     

Neural Processes Underlying the“Same”-“Different” Judgment of Two Simultaneously Presented Objects- An EEG Study

The present study investigated the neural processes underlying “same” and -“different” judgments for two simultaneously presented objects, that varied on one or both, of two dimensions: color and shape. Participants judged whether or not the two objects were “same” or “different” on either the color dimension (color task) or the shape dimension (shape task). The unattended irrelevant dimension of the objects was either congruent (same-same; different-different) or incongruent (same-different). ERP data showed a main effect of color congruency in the time window 190–260 ms post-stimulus presentation and a main effect of shape congruency in the time window 220–280 ms post-stimulus presentation in both color and shape tasks. The interaction between color and shape congruency in the ERP data occurred in a later time window than the two main effects, indicating that mismatches in task-relevant and task-irrelevant dimensions were processed automatically and independently before a response was selected. The fact that the interference of the task-irrelevant dimension occurred after mismatch detection, supports a confluence model of processing.     

Evidence for a specific internal representation of motion–force relationships during object manipulation

 Human subjects learned a tracking task which required them to point at a moving target with the free end of an inverted pendulum object. In order to determine how subjects represented this object internally, we studied learning interference between variants of this task in which the pendulum object had either stable or unstable dynamics. Using a novel method, agreement between possible internal representations of the two tasks was estimated by analysis of the motion-to-torque relationships experienced by each subject as they manipulated each object. It was possible to predict retention of the primary task on day 2 from our measure of agreement between primary and interfering tasks on day 1. This result suggests that the subjects learned the correct torque patterns to use to produce specific desired patterns of motion as they learned the balancing task. Surprisingly, the analyses indicate that retention was not impaired when similar motions of the two objects required retrieval of incompatible torque responses, but retention was impaired when similar patterns of motion in the two tasks required similar patterns of applied torque. These findings can be accounted for by a simple model of how multiple similar torque responses are selected and retrieved from memory when responses are freely chosen. Received: 20 December 2001 / Accepted in revised form: 25 July 2002 Correspondence to: C. D. Mah (e-mail: c-mah@northwestern.edu)     

EMG biofeedback and discriminative muscle control

The awareness model of biofeedback suggests that training teaches new skills or enhances performance at old skills, while the cognitive or feed-forward models suggest that biofeedback brings attention to the response of interest but does not actually increase task skill. In a test of the predictions made by these models, subjects were tested on one or more cross-modal matching tasks, provided brief training, and retested on the task(s). Thirty subjects participated in integer-matching tasks in which they were instructed to produce various levels of frontalis activity corresponding to the levels of a ratio scale. Forty-five subjects participated in a tone-matching task in which they tried to match their frontalis tension to the pitch of a tone. The results indicated that the groups receiving biofeedback training improved at the more difficult integer task and at the tone task. Subjects performed better on the integer tasks than at the tone task. Our findings suggest that an awareness model accounts for changes occurring during biofeedback training. However, an awareness model may be applicable only for tasks of moderate difficulty; for relatively easy tasks, a feed-forward model may be more appropriate. The clinical utility of cross-modal matching tasks is also described.This paper is based on a thesis conducted by the second author under the direction of the first author. Portions of this paper were presented at the annual meeting of the Association for Applied Psychophysiology and Biofeedback, March 1989, San Diego.     

Spatial and Feature-Based Attention in a Layered Cortical Microcircuit Model

Directing attention to the spatial location or the distinguishing feature of a visual object modulates neuronal responses in the visual cortex and the stimulus discriminability of subjects. However, the spatial and feature-based modes of attention differently influence visual processing by changing the tuning properties of neurons. Intriguingly, neurons'' tuning curves are modulated similarly across different visual areas under both these modes of attention. Here, we explored the mechanism underlying the effects of these two modes of visual attention on the orientation selectivity of visual cortical neurons. To do this, we developed a layered microcircuit model. This model describes multiple orientation-specific microcircuits sharing their receptive fields and consisting of layers 2/3, 4, 5, and 6. These microcircuits represent a functional grouping of cortical neurons and mutually interact via lateral inhibition and excitatory connections between groups with similar selectivity. The individual microcircuits receive bottom-up visual stimuli and top-down attention in different layers. A crucial assumption of the model is that feature-based attention activates orientation-specific microcircuits for the relevant feature selectively, whereas spatial attention activates all microcircuits homogeneously, irrespective of their orientation selectivity. Consequently, our model simultaneously accounts for the multiplicative scaling of neuronal responses in spatial attention and the additive modulations of orientation tuning curves in feature-based attention, which have been observed widely in various visual cortical areas. Simulations of the model predict contrasting differences between excitatory and inhibitory neurons in the two modes of attentional modulations. Furthermore, the model replicates the modulation of the psychophysical discriminability of visual stimuli in the presence of external noise. Our layered model with a biologically suggested laminar structure describes the basic circuit mechanism underlying the attention-mode specific modulations of neuronal responses and visual perception.     

Decision-Making under Ambiguity Is Modulated by Visual Framing,but Not by Motor vs. Non-Motor Context. Experiments and an Information-Theoretic Ambiguity Model

A number of recent studies have investigated differences in human choice behavior depending on task framing, especially comparing economic decision-making to choice behavior in equivalent sensorimotor tasks. Here we test whether decision-making under ambiguity exhibits effects of task framing in motor vs. non-motor context. In a first experiment, we designed an experience-based urn task with varying degrees of ambiguity and an equivalent motor task where subjects chose between hitting partially occluded targets. In a second experiment, we controlled for the different stimulus design in the two tasks by introducing an urn task with bar stimuli matching those in the motor task. We found ambiguity attitudes to be mainly influenced by stimulus design. In particular, we found that the same subjects tended to be ambiguity-preferring when choosing between ambiguous bar stimuli, but ambiguity-avoiding when choosing between ambiguous urn sample stimuli. In contrast, subjects’ choice pattern was not affected by changing from a target hitting task to a non-motor context when keeping the stimulus design unchanged. In both tasks subjects’ choice behavior was continuously modulated by the degree of ambiguity. We show that this modulation of behavior can be explained by an information-theoretic model of ambiguity that generalizes Bayes-optimal decision-making by combining Bayesian inference with robust decision-making under model uncertainty. Our results demonstrate the benefits of information-theoretic models of decision-making under varying degrees of ambiguity for a given context, but also demonstrate the sensitivity of ambiguity attitudes across contexts that theoretical models struggle to explain.     

Reading hidden intentions in the human brain

When humans are engaged in goal-related processing, activity in prefrontal cortex is increased. However, it has remained unclear whether this prefrontal activity encodes a subject's current intention. Instead, increased levels of activity could reflect preparation of motor responses, holding in mind a set of potential choices, tracking the memory of previous responses, or general processes related to establishing a new task set. Here we study subjects who freely decided which of two tasks to perform and covertly held onto an intention during a variable delay. Only after this delay did they perform the chosen task and indicate which task they had prepared. We demonstrate that during the delay, it is possible to decode from activity in medial and lateral regions of prefrontal cortex which of two tasks the subjects were covertly intending to perform. This suggests that covert goals can be represented by distributed patterns of activity in the prefrontal cortex, thereby providing a potential neural substrate for prospective memory. During task execution, most information could be decoded from a more posterior region of prefrontal cortex, suggesting that different brain regions encode goals during task preparation and task execution. Decoding of intentions was most robust from the medial prefrontal cortex, which is consistent with a specific role of this region when subjects reflect on their own mental states.     

No about face on houses in the fusiform face area!

Yovel and Kanwisher (this issue of Neuron) altered upright and inverted face and house characteristics during a same-different task. The right fusiform face area (FFA) was more active to faces than houses but, unlike behavior, was unaffected by spatial configuration or parts manipulations. These data raise interesting questions regarding the relationship of brain activation to observed behavior.     

Paired Bernoulli trials

Paired Bernoulli trials occur whenever an investigator records the presence of a particular characteristic at two sites on the same individual. While a study involving n subjects does not provide 2n independent pieces of information, neither does it provide only n pieces unless the characteristic must necessarily occur bilaterally. It is shown that the analysis of a model for sites in which the probability of occurrence at the second site given an occurrence at the first site is not functionally related to the probability of occurrence at the first site is equivalent to an analysis of counts of individuals grouped by whether the characteristic is absent, occurs unilaterally, or occurs bilaterally. It is shown that a test statistic proposed by Rosner (1982, Biometrics 38, 105-114) using a different model for such data can differ markedly from its corresponding likelihood-ratio statistic.