Motion Direction Discrimination Task Research Articles

Neural Mechanisms of Post-error Adjustments of Decision Policy in Parietal Cortex

Humans often slow down after mistakes (post-error slowing [PES]), but the neural mechanism and adaptive role of PES remain controversial. We studied changes in the neural mechanisms of decision making after errors in humans and monkeys that performed a motion direction discrimination task. We found that PES is mediated by two factors: a reduction in sensitivity to sensory information and an increase in the decision bound. Both effects are implemented through dynamic changes in the decision-making process. Neuronal responses in the monkey lateral intraparietal area revealed that bound changes are implemented by decreasing an evidence-independent urgency signal. They also revealed a reduction in the rate of evidence accumulation, reflecting reduced sensitivity. These changes in the bound and sensitivity provide a quantitative account of choices and response times. We suggest that PES reflects an adaptive increase of decision bound in anticipation of maladaptive reductions in sensitivity to incoming evidence.

A spiking neuron network model for the delayed motion direction discrimination task

Drawing the correct decision in a given situation usually depends on past experiences. While the neural basis of decision making per se has been studied extensively, how a memory of a previous situation could influence a later decision is less clear. One behavioral paradigm for investigating decision making in relation to an earlier reference is the delayed motion direction discrimination task (DMD) [1]. In this task, a variable reference direction is first presented to the subject by displaying a coherent random dot kinematograms (RDK). After memorizing, a delayed presentation of the test direction (RDK) follows and the subject needs to report whether the test direction is clockwise (CW) or anticlockwise (ACW) rotated in relation to the reference direction (Figure ​(Figure1A).1A). Although phenomenological models have been proposed, the underlying neural mechanism remains relatively unknown. Here, we hypothesize that a mechanism based on the idea of asymmetric connections similar to those used in neural networks explaining angular path integration in the head-direction system [2], might explain the behavioral results. Figure 1 A. DMD task: either ACW or CW has to be reported in relation to the reference. B. Network structure. Pyramid cells of WMC (CPC and APC) are arranged on a circle according to their preferred motion directions and with rotation invariant Gaussian shaped ... To test this hypothesis, we build a spiking neuron network model and investigate whether it can solve the DMD task. The network consists of three parts (Figure ​(Figure1.B):1.B): 1) a working memory circuit (WMC) 2) two information extraction circuits, referred to as clockwise-preferred circuit (CPC) and anticlockwise-preferred circuit (APC) respectively, and 3) a decision-making circuit. At the core of the network is the assumption of an asymmetric offset and rotational invariance of the connectivity profile. The former ensures that CPC (or APC) has stronger response when the test direction is CW (or ACW) rotated with respect to the reference direction and the latter guarantees the feasibility of the network under variable references. The simulations demonstrate that the proposed network is indeed capable of solving the DMD task (Figure ​(Figure1.C)1.C) showing a similar detection threshold (2°) as previous behavioral data [3]. Furthermore, the model correctly predicts that with higher similarity of reference and test direction or lower coherence level of the RDK, the performance gets worse (lower accuracy and longer reaction time). Our results suggest a possible neural mechanism for memory-guided decision making.

Interference effects of choice on confidence: Quantum characteristics of evidence accumulation

Decision-making relies on a process of evidence accumulation which generates support for possible hypotheses. Models of this process derived from classical stochastic theories assume that information accumulates by moving across definite levels of evidence, carving out a single trajectory across these levels over time. In contrast, quantum decision models assume that evidence develops over time in a superposition state analogous to a wavelike pattern and that judgments and decisions are constructed by a measurement process by which a definite state of evidence is created from this indefinite state. This constructive process implies that interference effects should arise when multiple responses (measurements) are elicited over time. We report such an interference effect during a motion direction discrimination task. Decisions during the task interfered with subsequent confidence judgments, resulting in less extreme and more accurate judgments than when no decision was elicited. These results provide qualitative and quantitative support for a quantum random walk model of evidence accumulation over the popular Markov random walk model. We discuss the cognitive and neural implications of modeling evidence accumulation as a quantum dynamic system.

Sharpened cortical tuning and enhanced cortico-cortical communication contribute to the long-term neural mechanisms of visual motion perceptual learning

Much has been debated about whether the neural plasticity mediating perceptual learning takes place at the sensory or decision-making stage in the brain. To investigate this, we trained human subjects in a visual motion direction discrimination task. Behavioral performance and BOLD signals were measured before, immediately after, and two weeks after training. Parallel to subjects' long-lasting behavioral improvement, the neural selectivity in V3A and the effective connectivity from V3A to IPS (intraparietal sulcus, a motion decision-making area) exhibited a persistent increase for the trained direction. Moreover, the improvement was well explained by a linear combination of the selectivity and connectivity increases. These findings suggest that the long-term neural mechanisms of motion perceptual learning are implemented by sharpening cortical tuning to trained stimuli at the sensory processing stage, as well as by optimizing the connections between sensory and decision-making areas in the brain.

Cortical configuration by stimulus onset visual evoked potentials (SO-VEPs) predicts performance on a motion direction discrimination task

The slowing of information processing, a hallmark of cognitive aging, has several origins. Previously we reported that in a motion direction discrimination task, older as compared to younger participants showed prolonged non-decision time, an index of an early perceptual stage, while in motion onset visual evoked potentials (MO-VEPs) the P1 component was enhanced and N2 was diminished. We did not find any significant correlations between behavioral and MO-VEP measures. Here, we investigated the role of age in encoding and perceptual processing of stimulus onset visually evoked potentials (SO-VEPs). Twelve healthy adults (age<55years) and 19 elderly (age>55years) performed a motion direction discrimination task during EEG recording. Prior to motion, the stimulus consisted of a static cloud of white dots on a black background. As expected, SO-VEPs evoked well defined P1, N1, and P2 components. Elderly participants as compared to young participants showed increased P1 amplitude while their P2 amplitude was reduced. In addition elderly participants showed increased latencies for P1 and N1 components. Contrary to the findings with MO-VEPs, SO-VEP parameters were significant predictors of average response times and diffusion model parameters. Our electrophysiological results support the notion that slowing of information processing in older adults starts at the very beginning of encoding in visual cortical processing, most likely in striate and extrastriate visual cortices. More importantly, the earliest SO-VEP components, possibly reflecting configuration of visual cortices and encoding processes, predict subsequent prolonging and tardiness of perceptual and higher-level cognitive processes.

Moderate acute alcohol intoxication has minimal effect on surround suppression measured with a motion direction discrimination task.

A well-studied paradox of motion perception is that, in order to correctly judge direction in high-contrast stimuli, subjects need to observe motion for longer in large stimuli than in small stimuli. This effect is one of several perceptual effects known generally as "surround suppression." It is usually attributed to center-surround antagonism between neurons in visual cortex, believed to be mediated by GABA-ergic inhibition. Accordingly, several studies have reported that this index of surround suppression is reduced in groups known to have reduced GABA-ergic inhibition, including older people and people with schizophrenia and major depressive disorder. In this study, we examined the effect on this index of moderate amounts of ethanol alcohol. Among its many effects on the nervous system, alcohol potentiates GABA-ergic transmission. We therefore hypothesized that it should further impair the perception of motion in large stimuli, resulting in a stronger surround-suppression index. This prediction was not borne out. Alcohol consumption slightly worsened duration thresholds for both large and small stimuli, but their ratio did not change significantly.

Behavioral consequences of perceptual decision-making in oculomotor brain structures

Neurons in several oculomotor brain areas (such as the lateral intraparietal area and superior colliculus) carry a multitude of signals. Even within a single task, individual neurons may exhibit responses related to visual/sensory events, decision formation, and saccade execution. Little is known about whether these signals interact and if such interactions have functional consequences. To test for interactions between decision-making and saccade execution signals, we used a behavioral dual-task paradigm that measured saccade reaction time (SRT) to a decision-irrelevant target while observers conducted a motion direction discrimination task. Observers (n=5) judged the direction (leftward versus rightward) of a random dot motion stimulus (of variable coherence; speed: 5 °/s). At the offset of the dots, a target appeared either left or right side of the fixation point (displaced by 20°). Observers were instructed to make an eye movement to the target as quickly as possible. After the eye movement, the direction of preceding dot motion was reported with a button press. We tested whether the SRT to the target was affected by the direction and strength of motion stimuli presented during the direction-discrimination task. Indeed, SRTs were faster on congruent trials (when the direction of motion was same as the saccade direction) compared to incongruent trials (F1,4=26.23, p<0.01). Furthermore, SRTs progressively decreased with increased coherence (F4,16=5.45, p<0.05). Thus, simple visually-guided saccades were affected by the ongoing buildup of activity related to decision formation, in a manner that was direction-selective and parametrically affected by motion strength. Our results are not due to the mere presence of motion stimuli because the dependencies on coherence and directional congruency were eliminated in a single-task (saccade only) control experiment. Revealing such interactions between decision making and saccade executions suggests that these two types of signals cannot be completely demixed in neural circuitry. Meeting abstract presented at VSS 2014

Leakage of decision uncertainty into movement execution in Parkinson’s disease?

The concept of segregated basal ganglia-cortical loops entails that functional disturbances may result from abnormal processing within loops, but also from abnormal communication between loops. Cognitive and motor processes subserved by different basal ganglia-frontal loops may interfere with one another as a result of such abnormal communication, leakage, between loops. In Parkinson's disease, movement execution has been found susceptible to decision uncertainty, attributed to this mechanism. Here, we evaluate whether this mechanism of abnormal coupling or leakage extends to perceptual decision-making with trial-by-trial control of decision uncertainty. We examined 10 Parkinson's disease (PD) patients and healthy control subjects in a random-dot motion direction discrimination task with concurrent EEG recording. Random-dot motion was manipulated to make direction discrimination easy or difficult. Reaction times (RT) and movement times (MT) were recorded, and EEG was analysed to extract movement-related potentials. Easy versus difficult direction discrimination produced robust, equally large RT differences in patients and controls (>400 ms), along with a marked difference in error rates, confirming the efficacy of the task. Effects of easy versus difficult discrimination on MT were comparatively small (<50 ms) and did not differ between groups, despite robustly slower MT in patients. Lateralised movement-related EEG potentials reproduced the MT difference between patients and controls. Together, the results do not demonstrate an enhanced effect of decision uncertainty onto movement execution in PD. We surmise that leakage of decision uncertainty into movement execution is probably task-dependent, consistent with the view that the degree to which partial information is allowed to influence the motor system is under strategic control.

Biological Motion Processing in Schizotypic and Autistic Traits

Previous research has shown that motion processing is significantly impaired in both autistic and schizophrenic patients. One specific area of motion perception that is affected by both disorders is the processing of biological motion. Stimuli that are often used to investigate biological motion perception are point-light walkers (PLW), for which point-lights are attached to the joints of a moving person, which alone are enough to perceive the human figure. PLWs are useful stimuli to investigate biological motion perception, because they contain the local motion information of each dot, and in addition, by grouping the local elements of the walkers into a global form, they have a high-level interpretation of a moving person (normal walker). By scrambling the positions of the points on the screen, the local motion of each dot is preserved while obscuring the underlying form (scrambled walker). Similarly, by randomizing the position of the dots along the underlying skeleton each frame of the moving sequence, the local image motion is lost, whereas the global form of the walker is preserved (random-position walker). Also inverting the walker in a way that it appears to be walking on the ceiling can obscure the global form of the walker (inverted walker). Using these four kinds of walkers, it is possible to investigate the relative contribution of form and motion information to biological motion perception using one single paradigm. We have successfully used these walkers before to investigate biological motion perception in ageing. Here, we tested differences in biological motion processing in healthy young people with different schizotypic (N=38) and autistic traits (N=35). We asked participants to perform a biological motion direction discrimination task for normal, inverted, scrambled and random-position walkers. In addition, they had to complete questionnaires on autistic and schizotypic traits. Using both reaction time and accuracy measures we found differences for processing local motion and global form information between participants with high or low scores on both questionnaires.

Transfer in motion perceptual learning depends on the difficulty of the training task

One hypothesis in visual perceptual learning is that the amount of transfer depends on the difficulty of the training and transfer tasks (Ahissar & Hochstein, 1997; Liu, 1995, 1999). Jeter, Dosher, Petrov, and Lu (2009), using an orientation discrimination task, challenged this hypothesis by arguing that the amount of transfer depends only on the transfer task but not on the training task. Here we show in a motion direction discrimination task that the amount of transfer indeed depends on the difficulty of the training task. Specifically, participants were first trained with either 4° or 8° direction discrimination along one average direction. Their transfer performance was then tested along an average direction 90° away from the trained direction. A variety of transfer measures consistently demonstrated that transfer performance depended on whether the participants were trained on 4° or 8° directional difference. The results contradicted the prediction that transfer was independent of the training task difficulty.

Aging effects on visual evoked potentials (VEPs) for motion direction discrimination

Age-related declines in motion perception have been well documented. We investigated the impact of age on electrophysiological correlates of motion perception, namely the P1 and N2 components of motion onset visual evoked potentials (MO-VEPs). Additionally, we used a model of response times based on the diffusion model to pinpoint the cognitive processes affected by aging. Twelve healthy adults (age <55years) and 19 elderly (age >55years) performed a motion direction discrimination task during EEG recording. Behaviorally, younger and older participants had similar, high accuracy rates — 98% correct, but older adults exhibited 85ms longer response times. Fitting behavioral results with a diffusion model revealed differences between young adults and elderly in non-decision time, which we argue reflects an early perceptual stage. Electrophysiologically, aging effects were present at MO-VEPs P1 and N2 components at the posterior sites. For the P1 component, older as compared to younger adults showed greater topographical voltage distribution. For the N2 component of elderly as compared to young adults we found delayed onsets and diminished amplitudes. We did not find any significant correlations between behavioral and MO-VEP measures. However, regression analysis showed that N2 amplitude and latency were significant age predictors. Overall, our results indicate that in motion perception, age-related changes occur in early stages of visual processing, most likely in striate and extrastriate visual cortices.

The benefits of cholinergic enhancement during perceptual learning are long-lasting

The neurotransmitter acetylcholine (ACh) regulates many aspects of cognition, including attention and memory. Previous research in animal models has shown that plasticity in sensory systems often depends on the behavioral relevance of a stimulus and/or task. However, experimentally increasing ACh release in the cortex can result in experience-dependent plasticity, even in the absence of behavioral relevance. In humans, the pharmacological enhancement of ACh transmission by administration of the cholinesterase inhibitor donepezil during performance of a perceptual task increases the magnitude of perceptual learning (PL) and its specificity to physical parameters of the stimuli used for training. Behavioral effects of PL have previously been shown to persist for many months. In the present study, we tested whether enhancement of PL by donepezil is also long-lasting. Healthy human subjects were trained on a motion direction discrimination task during cholinergic enhancement, and follow-up testing was performed 5–15 months after the end of training and without additional drug administration. Increases in performance associated with training under donepezil were evident in follow-up retesting, indicating that cholinergic enhancement has beneficial long-term effects on PL. These findings suggest that cholinergic enhancement of training procedures used to treat clinical disorders should improve long-term outcomes of these procedures.

A window of perception when diverting attention? Enhancing recognition for explicitly presented, unattended, and irrelevant stimuli by target alignment.

Research has demonstrated that irrelevant suprathreshold motion stimuli that are aligned with attended targets in a separate task, fail to illicit inhibitory control in a subsequent motion direction discrimination task (Tsushima, Seitz, & Watanabe, 2008). We extended these findings to conditions involving higher exposure levels to a more salient stimulus (written words) in an inattentional blindness paradigm. Across three experiments, participants were required to respond to immediate picture repetitions in a stream of serially presented line drawings, while at the same time ignore a simultaneously presented stream of superimposed words. Immediately following, a surprise test was given that measured recognition for the unattended words. Words that had appeared simultaneously with a repeated picture in the repetition detection task were not inhibited, but instead recognized significantly more often than words that had appeared with nonrepeating pictures. These findings support the notion that when attention is taxed, recognition for target-aligned task-irrelevant semantic items can be enhanced in a subsequent recognition task. This indicates a learning effect for frequently exposed, high-level irrelevant-stimuli that were temporally aligned with a relevant item in a separate task.

Low-level processing deficits underlying poor contrast sensitivity for moving plaids in anisometropic amblyopia

Many studies using random dot kinematograms have indicated a global motion processing deficit originated from extrastriate cortex, specifically middle temporal area (MT) and media superior temporal area (MST), in patients with amblyopia. However, the nature of this deficit remains unclear. To explore whether the ability of motion integration is impaired in amblyopia, contrast sensitivity for moving plaids and their corresponding component gratings were measured over a range of stimulus durations and spatial and temporal frequencies in 10 control subjects and 13 anisometropic amblyopes by using a motion direction discrimination task. The results indicated a significant loss of contrast sensitivity for moving plaids as well as for moving gratings at intermediate and high spatial frequencies in amblyopic eyes (AEs). Additionally, we found that the loss of contrast sensitivity for moving plaids was statistically equivalent to that for moving component gratings in AEs, that is, the former could be almost completely accounted for by the latter. These results suggest that the integration of motion information conveyed by component gratings of moving plaids may be intact in anisometropic amblyopia, and that the apparent deficits in contrast sensitivity for moving plaids in anisometropic amblyopia can be almost completely attributed to those for gratings, that is, low-level processing deficits.

Age Related Changes to Perceptual Surround Suppression of Moving Stimuli

Perceptual analogues of centre-surround suppression have been applied as indirect measures of cortical inhibitory function in several clinical disorders. Two tasks have been used: a centre-surround contrast perception task and a motion direction discrimination task, where the stimulus size and contrast is varied to measure surround suppression effects. The tasks are markedly different, yet previous literature implies that both measures indirectly assess inhibitory function and that results will be complementary. This is not the case for age-related effects on surround suppression, however, as previous reports using the different measures are conflicting. Here we use a low-spatial frequency, drifting grating version of the centre-surround contrast perception task, and compare results to those obtained with the motion direction task in a single group of older observers. Older adults demonstrate significantly increased perceptual surround suppression of contrast for drifting, high contrast stimuli. Using the motion discrimination task, older observers showed similar amounts of surround suppression for the largest stimulus. This study confirms that visual surround suppression is altered by ageing. The complexity of neuronal systems involved in centre-surround interactions makes it unlikely that a single perceptual task will be sufficient to describe the effects of clinical disorders on surround suppression.

Quantitative measurement of interocular suppression in children with amblyopia

In this study we explored the possibility of using a dichoptic global motion technique to measure interocular suppression in children with amblyopia. We compared children (5–16years old) with unilateral anisometropic and/or strabismic amblyopia to age-matched control children. Under dichoptic viewing conditions, contrast interference thresholds were determined with a global motion direction–discrimination task. Using virtual reality goggles, high contrast signal dots were presented to the amblyopic eye, while low contrast noise dots were presented to the non-amblyopic fellow eye. The contrast of the noise dots was increased until discrimination of the motion direction of the signal dots reached chance performance. Contrast interference thresholds were significantly lower in the strabismic group than in the anisometropic and control group. Our results suggest that interocular suppression is stronger in strabismic than in anisometropic amblyopia.

Prestimulus hemodynamic activity in dorsal attention network is negatively associated with decision confidence in visual perception

Attention is thought to improve most aspects of perception. However, we recently showed that, somewhat surprisingly, endogenous attention can also lead to low subjective perceptual ratings (Rahnev et al., 2011). Here we investigated the neural basis of this effect and tested whether spontaneous fluctuations of the attentional state can lead to low confidence in one's perceptual decision. We measured prestimulus functional magnetic resonance imaging activity in the dorsal attention network and used that activity as an index of the level of attention involved in a motion direction discrimination task. Extending our previous findings, we showed that low prestimulus activity in the dorsal attention network, which presumably reflected low level of attention, was associated with higher confidence ratings. These results were explained by a signal detection theoretic model in which lack of attention increases the trial-by-trial variability of the internal perceptual response. In line with the model, we also found that low prestimulus activity in the dorsal attention network was associated with higher trial-by-trial variability of poststimulus peak activity in the motion-sensitive region MT+. These findings support the notion that lack of attention may lead to liberal subjective perceptual biases, a phenomenon we call "inattentional inflation of subjective perception."

Visibility versus accountability in pooling local motion signals into global motion direction

The human observer is surprisingly inaccurate in discriminating proportions between two spatially overlapping sets of randomly distributed elements moving in opposite directions. It was shown that observers took into account an equivalent of 74% of all moving elements when the task was to estimate their relative number, but only an equivalent of 21% of the same elements when the task was to discriminate between opposite directions. It was concluded that, in the motion direction discrimination task, a large proportion of the signal from all of the elements was inaccessible to the observers, whereas the majority of the signal was accessible in a numerosity task. This type of perceptual limitation belongs to the attentional blindness category, where a strong sensory signal cannot be noticed when processing is diverted by parallel events. In addition, we found no evidence for the common-fate principle, as the ability to discriminate numerical proportions remained the same, irrespective of whether all estimated elements were moving coherently in one direction or unpredictably in opposite directions.

Dissociable Perceptual Learning Mechanisms Revealed by Diffusion-Model Analysis

Performance on perceptual tasks improves with practice. Most theories address only accuracy data and tacitly assume that perceptual learning is a monolithic phenomenon. The present study pioneers the use of response time distributions in perceptual learning research. The 27 observers practiced a visual motion-direction discrimination task with filtered-noise textures for four sessions with feedback. Session 5 tested whether the learning effects transferred to the orthogonal direction. The diffusion model (Ratcliff, Psychological Review, 85, 59–108, 1978) achieved good fits to the individual response time distributions from each session and identified two distinct learning mechanisms with markedly different specificities. A stimulus-specific increase in the drift-rate parameter indicated improved sensory input to the decision process, and a stimulus-general decrease in nondecision time variability suggested improved timing of the decision process onset relative to stimulus onset (which was preceded by a beep). A traditional d’ analysis would miss the latter effect, but the diffusion-model analysis identified it in the response time data.

Neural correlates of evidence accumulation in a perceptual decision task

Sequential sampling models provide a useful framework for understanding human decision making. A key component of these models is an evidence accumulation process in which information is accrued over time to a threshold, at which point a choice is made. Previous neurophysiological studies on perceptual decision making have suggested accumulation occurs only in sensorimotor areas involved in making the action for the choice. Here we investigated the neural correlates of evidence accumulation in the human brain using functional magnetic resonance imaging (fMRI) while manipulating the quality of sensory evidence, the response modality, and the foreknowledge of the response modality. We trained subjects to perform a random dot motion direction discrimination task by either moving their eyes or pressing buttons to make their responses. In addition, they were cued about the response modality either in advance of the stimulus or after a delay. We isolated fMRI responses for perceptual decisions in both independently defined sensorimotor areas and task-defined nonsensorimotor areas. We found neural signatures of evidence accumulation, a higher fMRI response on low coherence trials than high coherence trials, primarily in saccade-related sensorimotor areas (frontal eye field and intraparietal sulcus) and nonsensorimotor areas in anterior insula and inferior frontal sulcus. Critically, such neural signatures did not depend on response modality or foreknowledge. These results help establish human brain areas involved in evidence accumulation and suggest that the neural mechanism for evidence accumulation is not specific to effectors. Instead, the neural system might accumulate evidence for particular stimulus features relevant to a perceptual task.