Sensory Discrimination Research Articles

Sensory Discrimination Tests for Low- and High-Strength Alcohol

Research is limited on consumers’ ability to detect perceptible sensory differences between low- and high-strength alcoholic beverages. This study, therefore, conducted three pilot experiments using ISO sensory analysis methods to assess accuracy for evaluating beverages of different strengths. Participants were food production professionals trained in sensory analysis. Experiment 1 used a wide-range discrimination test to estimate low- to high-strength beverages (0–60% alcohol by volume (ABV) in 10% intervals). Experiment 2 included a narrower range of intermediate to high strengths (25–45% ABV in 5% intervals). Experiment 3 used 3-alternative forced choice tests (ISO 13301) to discriminate between beverages of varying strengths. Experiment 1 (n = 16) indicated that estimation ability was dependent upon the beverages’ ABV; as ABV increased, estimation significantly decreased (p < 0.005). These findings were not replicated in Experiment 2 (n = 13). In Experiment 3 (n = 17), a significant perceptible difference between high- and low-strength samples was observed in two of nine conditions (35% vs. 31% ABV (p = 0.009); 41% vs. 37% ABV (p = 0.037)). While people can detect large differences in beverage ABVs, they may have a moderate to poor ability to discriminate between beverages of similar strengths. These findings provide support for public health interventions that promote lower-strength alcoholic beverages.

A Randomized Crossover Trial of Acceptability of Quadruple-Fortified Salt in Women and their Households in Southern India

BackgroundDouble-fortified salt (DFS; iron, iodine) improved iron status in randomized trials and was incorporated into India’s social safety net programs, suggesting opportunities to address other micronutrient deficiencies. ObjectivesTo evaluate acceptability of quadruple-fortified salt (QFS; iron, iodine, folic acid, vitamin B12) in women and their households, using a randomized crossover trial design and triangle tests. MethodsWomen 18-49y (n=77) and their households were randomized to receive QFS or DFS in a randomized crossover design over a 3-week period (week 1: QFS/DFS, 2: iodized salt, 3: DFS/QFS). Each week, participants completed a 9-point hedonic questionnaire (1=dislike extremely to 9=like extremely) to evaluate five sensory domains (color, odor, taste, texture, overall acceptability) of the intervention, and remaining salt was weighed using a digital scale. Triangle tests were conducted among women to evaluate sensory discrimination of salt consumed in rice dishes prepared using standardized recipes. Mixed models were used to examine hedonic ratings and salt use; salt type, sequence, and period were included as fixed effects, and household was included as a random effect. Binomial tests were used to evaluate sensory discrimination of salt type in triangle tests. ResultsMean hedonic ratings for most of the five sensory domains were ≥7 (like moderately) and did not differ by salt type (overall acceptability mean [SD]: QFS: 7.8 [0.7] vs. DFS: 7.7 [1.2]; p=0.68). Household salt use (weighed) did not differ by salt type. During the 3-week intervention period, weighed salt use and hedonic ratings significantly increased, indicating a period effect independent of salt type or sequence. In triangle tests, rice samples prepared with QFS, DFS, or iodized salt were not distinguishable. ConclusionAcceptability of QFS was high, based on individual hedonic ratings and weighed household salt use. Rice dishes prepared with DFS, QFS, and iodized salt were not distinguishable. Findings informed the design of a randomized trial of QFS in this population. Registration numbersNCT03853304 and REF/2019/03/024479.

Association between biological markers and somatic pain

Pain, as one of the major clinical and social problems, still lacks effective objective evaluation indicators. At present, nearly one in five adults suffer from different types and different parts of pain. An important feature of clinical pain is persistent pain, in addition to sensory discrimination processes, it involves a range of brain regions involved in top-down cognitive and emotional processing. However, clinical pain is often affected by multiple factors and is difficult to assess objectively. Recently, blood, urine, cerebrospinal fluid, and biopsy tissue have been identified using novel, sensitive, and specific protein analysis methods in an attempt to detect changes in biological markers associated with different pain types. This paper will summarize the biological markers related to different parts of pain in the latest relevant studies at home and abroad and focus on the application prospect of such biological markers in the diagnosis, treatment, and prognosis evaluation of the pain.

Somatosensory Mapping Using a Novel Sensory Discrimination Task: Technical Note.

Although diffuse gliomas in the primary somatosensory cortex (S1) are often considered resectable, gliomas in the primary motor cortex require motor mapping to preserve motor function. Recent evidence indicates that some somatosensory cortex neurons may trigger motor responses, necessitating refined somatosensory mapping techniques. Using piezoelectric tactile stimulators on patients' faces and hands, we delivered 25 Hz vibrations and prompted patients to discriminate between dermatomes. Testing included areas contralateral to tumor-infiltrated and to non-tumor-infiltrated cortical regions. Sensory thresholds were determined by reducing stimulus intensity based on performance. Intraoperatively, electrocorticography electrode arrays were used to map sensory responses, and postoperative assessments evaluated sensory outcomes. The high-grade glioma case involved a 61-year-old man with right-sided weakness and numbness with a left parietal mass on MRI. Preoperative testing showed that the average vibratory detection threshold of the hand contralateral to the suspected tumor site was significantly higher than that of the hand contralateral to healthy cortex (P < .001). Intraoperative mapping confirmed the absence of functional involvement in cortical structures overlying the tumor. Postoperative imaging confirmed gross total resection, and sensory vibratory thresholds were normalized (P = .51). The low-grade glioma case included a 54-year-old man with a left parietal nonenhancing mass on MRI. No baseline sensory impairments were found on preoperative testing. Intraoperative mapping identified motor and sensory cortices, guiding tumor resection while preserving motor function. Postoperative MRI confirmed near-total resection, but new sensory impairments were noted in the hand and face contralateral to the resection site (P < .001). These deficits resolved by postoperative day 11, with no evidence of tumor progression on follow-up imaging. The sensory discrimination task provides a quantifiable method for assessing sensory changes and functional outcomes related to glioma. This technique enhances our understanding of how glioma infiltration remodels sensory systems and affects clinical outcomes in patients.

Mitigation of polycyclic aromatic hydrocarbons (PAHs) in roasted beef patties by cold plasma treatment and products quality evaluation

The cold plasma (CP) technique was applied to alleviate the contamination of polycyclic aromatic hydrocarbon (PAH) in this investigation. Two different CP treatments methods were implemented in the production of beef patties, to investigate their inhibition and degradation capacity on PAHs. With 5 different cooking oils and fats addition, the inhibition mechanism of in-package cold plasma (ICP) pretreatment was explored from the aspect of raw patties fatty acids composition variation. The results of principal component analysis showed that the first two principal components accounted for more than 80 % of the total variation in the original data, indicating that the content of saturated fatty acids was significantly positively correlated with the formation of PAHs. ICP pretreatment inhibited the formation of PAHs by changing the composition of fatty acids, which showed that the total amount of polyunsaturated fatty acids decreased and the total amount of monounsaturated fatty acids increased. Sensory discrimination tests demonstrated there were discernable differences between 2 CP treated samples and the controls, utilization of the ICP pretreatment in meat products processing was expected to achieve satisfying eating quality. In conclusion, CP treatment degraded PAHs through stepwise ring-opening oxidation in 2 reported pathways, the toxicity of PAHs contaminated products was alleviated after CP treatment.

Benchmarking automation-aided performance in a forensic face matching task

Carragher and Hancock (2023) investigated how individuals performed in a one-to-one face matching task when assisted by an Automated Facial Recognition System (AFRS). Across five pre-registered experiments they found evidence of suboptimal aided performance, with AFRS-assisted individuals consistently failing to reach the level of performance the AFRS achieved alone. The current study reanalyses these data (Carragher and Hancock, 2023), to benchmark automation-aided performance against a series of statistical models of collaborative decision making, spanning a range of efficiency levels. Analyses using a Bayesian hierarchical signal detection model revealed that collaborative performance was highly inefficient, falling closest to the most suboptimal models of automation dependence tested. This pattern of results generalises previous reports of suboptimal human-automation interaction across a range of visual search, target detection, sensory discrimination, and numeric estimation decision-making tasks. The current study is the first to provide benchmarks of automation-aided performance in the one-to-one face matching task.

Performance of Adults With &amp; Without Sensory Processing Challenges on the Sensory Processing 3 Dimensions Assessment

Abstract Date Presented 03/22/24 Scores from the Sensory Processing 3 Dimensions (SP3D) Assessment were used to examine sensory modulation, discrimination, praxis, and postural functions, along with associated occupational performance problems in a sample of adults with and without sensory processing challenges. Primary Author and Speaker: Shelley Mulligan Additional Authors and Speakers: Sarah A. Schoen

Goal-directed learning is multidimensional and accompanied by diverse and widespread changes in neocortical signaling.

New tasks are often learned in stages with each stage reflecting a different learning challenge. Accordingly, each learning stage is likely mediated by distinct neuronal processes. And yet, most rodent studies of the neuronal correlates of goal-directed learning focus on individual outcome measures and individual brain regions. Here, we longitudinally studied mice from naïve to expert performance in a head-fixed, operant conditioning whisker discrimination task. In addition to tracking the primary behavioral outcome of stimulus discrimination, we tracked and compared an array of object-based and temporal-based behavioral measures. These behavioral analyses identify multiple, partially overlapping learning stages in this task, consistent with initial response implementation, early stimulus-response generalization, and late response inhibition. To begin to understand the neuronal foundations of these learning processes, we performed widefield Ca2+ imaging of dorsal neocortex throughout learning and correlated behavioral measures with neuronal activity. We found distinct and widespread correlations between neocortical activation patterns and various behavioral measures. For example, improvements in sensory discrimination correlated with target stimulus evoked activations of response-related cortices along with distractor stimulus evoked global cortical suppression. Our study reveals multidimensional learning for a simple goal-directed learning task and generates hypotheses for the neuronal modulations underlying these various learning processes.

Amygdala and Cortex Relationships during Learning of a Sensory Discrimination Task.

During learning of a sensory discrimination task, the cortical and subcortical regions display complex spatiotemporal dynamics. During learning, both the amygdala and cortex link stimulus information to its appropriate association, for example, a reward. In addition, both structures are also related to nonsensory parameters such as body movements and licking during the reward period. However, the emergence of the cortico-amygdala relationships during learning is largely unknown. To study this, we combined wide-field cortical imaging with fiber photometry to simultaneously record cortico-amygdala population dynamics as male mice learn a whisker-dependent go/no-go task. We were able to simultaneously record neuronal populations from the posterior cortex and either the basolateral amygdala (BLA) or central/medial amygdala (CEM). Prior to learning, the somatosensory and associative cortex responded during sensation, while amygdala areas did not show significant responses. As mice became experts, amygdala responses emerged early during the sensation period, increasing in the CEM, while decreasing in the BLA. Interestingly, amygdala and cortical responses were associated with task-related body movement, displaying significant responses ∼200 ms before movement initiation which led to licking for the reward. A correlation analysis between the cortex and amygdala revealed negative and positive correlation with the BLA and CEM, respectively, only in the expert case. These results imply that learning induces an involvement of the cortex and amygdala which may aid to link sensory stimuli with appropriate associations.

Feasibility of adopting imperfect produce in on-site foodservice: expert opinions and consumer sensory discrimination

PurposeThis research aims to investigate the feasibility of imperfect produce use in the on-site foodservice management industry.Design/methodology/approachStudy 1 explored experts’ perspectives via expert interviews on the use of imperfect produce in on-site foodservice operations, acceptability, and willingness to choose imperfect produce. Study 2, a sensory discrimination test, was performed with 100 consumers.FindingsStudy 1 yielded seven themes with managerial recommendations: appearance perception, customer value perception, operational difficulties, concerns for the world, food safety concerns, corporate advantages, and implementation. Study 2 found that participants were willing to choose menu items prepared with imperfect produce over those prepared with perfect produce. The ability to taste differences depended on the type of produce; participants could not taste differences between tangerines but could taste differences between apples and pears.Research limitations/implicationsThe findings of this study suggested that the psychological barriers of imperfect produce impact managers’ perceptions and decision-making processes. It is recommended that operators communicate with consumers about imperfect produce, its waste reduction benefits, and its quality.Originality/valueThis study shows that taste perception could be influenced by how imperfectness is described. Thus, appropriate marketing strategies could improve consumer acceptance of imperfect produce.

Profile of Sensory Integration Disorders in Migraine Patients-New Perspectives of Therapy.

Background: The involvement of sensory integration disorders in the pathophysiology of migraine has been suggested. This study aims to analyze the relationship between symptoms of sensory integration disorders and migraine in a broad scope, including all sensory domains, and examine its impact on migraine attacks. Methods: The study included 372 people diagnosed with migraine. The Daniel Travis Questionnaire was used to assess symptoms of sensory integration disorders and their severity across six domains. The relationships between the severity of these symptoms and headache features, as well as accompanying headache symptoms, were the subject of statistical analysis. Results: Current impairment in all sensory domains was significantly associated with headaches exacerbated by everyday life activities. A significant inverse relationship was found between the occurrence of throbbing headaches and symptoms of sensory integration disorders in terms of current sensory discrimination, current motor skills, and current emotional/social skills. Past under-responsiveness and past disturbances in emotional/social abilities were significantly associated with migraine aura. Conclusions: The severity of symptoms of sensory integration disorders affects the clinical picture of migraine. The significant association between migraine and emotional/social disorders, as well as under-responsiveness in the past, needs further research to assess whether this is a cause-and-effect relationship. There is a need for in-depth diagnostics of sensory integration disorders in migraine patients, which could be an additional target of their therapy.

Coexistence of state, choice, and sensory integration coding in barrel cortex LII/III

During perceptually guided decisions, correlates of choice are found as upstream as in the primary sensory areas. However, how well these choice signals align with early sensory representations, a prerequisite for their interpretation as feedforward substrates of perception, remains an open question. We designed a two alternative forced choice task (2AFC) in which male mice compared stimulation frequencies applied to two adjacent vibrissae. The optogenetic silencing of individual columns in the primary somatosensory cortex (wS1) resulted in predicted shifts of psychometric functions, demonstrating that perception depends on focal, early sensory representations. Functional imaging of layer II/III single neurons revealed mixed coding of stimuli, choices and engagement in the task. Neurons with multi-whisker suppression display improved sensory discrimination and had their activity increased during engagement in the task, enhancing selectively representation of the signals relevant to solving the task. From trial to trial, representation of stimuli and choice varied substantially, but mostly orthogonally to each other, suggesting that perceptual variability does not originate from wS1 fluctuations but rather from downstream areas. Together, our results highlight the role of primary sensory areas in forming a reliable sensory substrate that could be used for flexible downstream decision processes.

Goal-Directed Learning is Multidimensional and Accompanied by Diverse and Widespread Changes in Neocortical Signaling.

New tasks are often learned in stages with each stage reflecting a different learning challenge. Accordingly, each learning stage is likely mediated by distinct neuronal processes. And yet, most rodent studies of the neuronal correlates of goal-directed learning focus on individual outcome measures and individual brain regions. Here, we longitudinally studied mice from naïve to expert performance in a head-fixed, operant conditioning whisker discrimination task. In addition to tracking the primary behavioral outcome of stimulus discrimination, we tracked and compared an array of object-based and temporal-based behavioral measures. These behavioral analyses identify multiple, partially overlapping learning stages in this task, consistent with initial response implementation, early stimulus-response generalization, and late response inhibition. To begin to understand the neuronal foundations of these learning processes, we performed widefield Ca2+ imaging of dorsal neocortex throughout learning and correlated behavioral measures with neuronal activity. We found distinct and widespread correlations between neocortical activation patterns and various behavioral measures. For example, improvements in sensory discrimination correlated with target stimulus evoked activations of licking-related cortices along with distractor stimulus evoked global cortical suppression. Our study reveals multidimensional learning for a simple goal-directed learning task and generates hypotheses for the neuronal modulations underlying these various learning processes.

Pan-cortical 2-photon mesoscopic imaging and neurobehavioral alignment in awake, behaving mice.

The flow of neural activity across the neocortex during active sensory discrimination is constrained by task-specific cognitive demands, movements, and internal states. During behavior, the brain appears to sample from a broad repertoire of activation motifs. Understanding how these patterns of local and global activity are selected in relation to both spontaneous and task-dependent behavior requires in-depth study of densely sampled activity at single neuron resolution across large regions of cortex. In a significant advance toward this goal, we developed procedures to record mesoscale 2-photon Ca2+ imaging data from two novel in vivo preparations that, between them, allow for simultaneous access to nearly all 0f the mouse dorsal and lateral neocortex. As a proof of principle, we aligned neural activity with both behavioral primitives and high-level motifs to reveal the existence of large populations of neurons that coordinated their activity across cortical areas with spontaneous changes in movement and/or arousal. The methods we detail here facilitate the identification and exploration of widespread, spatially heterogeneous neural ensembles whose activity is related to diverse aspects of behavior.

Pan-cortical 2-photon mesoscopic imaging and neurobehavioral alignment in awake, behaving mice

The flow of neural activity across the neocortex during active sensory discrimination is constrained by task-specific cognitive demands, movements, and internal states. During behavior, the brain appears to sample from a broad repertoire of activation motifs. Understanding how these patterns of local and global activity are selected in relation to both spontaneous and task-dependent behavior requires in-depth study of densely sampled activity at single neuron resolution across large regions of cortex. In a significant advance toward this goal, we developed procedures to record mesoscale 2-photon Ca2+ imaging data from two novel in vivo preparations that, between them, allow for simultaneous access to nearly all 0f the mouse dorsal and lateral neocortex. As a proof of principle, we aligned neural activity with both behavioral primitives and high-level motifs to reveal the existence of large populations of neurons that coordinated their activity across cortical areas with spontaneous changes in movement and/or arousal. The methods we detail here facilitate the identification and exploration of widespread, spatially heterogeneous neural ensembles whose activity is related to diverse aspects of behavior.

Enhancing touch sensibility with sensory electrical stimulation and sensory retraining

A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, our understanding of somatosensory interventions such as sensory electrical stimulation (SES) in neurorehabilitation is limited. We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment in healthy participants, setting a foundation for its potential application in stroke rehabilitation. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with 26 healthy participants who explored a set of three visually identical virtual textures—haptically rendered by a robotic device and that differed in their spatial period—while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance—assessed by the probability of correct responses—before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8–13 Hz) associated with sensory processing. We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced. Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.

Music training is related to late ERP modulation and enhanced performance during Simon task but not Stroop task.

Increasing evidence suggests that music training correlates with better performance in tasks measuring executive function components including inhibitory control, working memory and selective attention. The Stroop and Simon tasks measure responses to congruent and incongruent information reflecting cognitive conflict resolution. However, there are more reports of a music-training advantage in the Simon than the Stroop task. Reports indicate that these tasks may differ in the timing of conflict resolution: the Stroop task might involve early sensory stage conflict resolution, while the Simon task may do so at a later motor output planning stage. We hypothesize that musical experience relates to conflict resolution at the late motor output stage rather than the early sensory stage. Behavioral responses, and event-related potentials (ERP) were measured in participants with varying musical experience during these tasks. It was hypothesized that musical experience correlates with better performance in the Simon but not the Stroop task, reflected in ERP components in the later stage of motor output processing in the Simon task. Participants were classified into high- and low-music training groups based on the Goldsmith Musical Sophistication Index. Electrical brain activity was recorded while they completed visual Stroop and Simon tasks. The high-music training group outperformed the low-music training group on the Simon, but not the Stroop task. Mean amplitude difference (incongruent-congruent trials) was greater for the high-music training group at N100 for midline central (Cz) and posterior (Pz) sites in the Simon task and midline central (Cz) and frontal (Fz) sites in the Stroop task, and at N450 at Cz and Pz in the Simon task. N450 difference peaks occurred earlier in the high-music training group at Pz. Differences between the groups at N100 indicate that music training may be related to better sensory discrimination. These differences were not related to better behavioral performance. Differences in N450 responses between the groups, particularly in regions encompassing the motor and parietal cortices, suggest a role of music training in action selection during response conflict situations. Overall, this supports the hypothesis that music training selectively enhances cognitive conflict resolution during late motor output planning stages.

Focal changes in alpha oscillations during short-term memorization of pain: a high-density electroencephalogram study with source localization.

Memories of painful events constitute the basis for assessing patients' pain. This study explores the brain oscillatory activity during short-term memorization of a nociceptive stimulus. High-density EEG activity (128 electrodes) was recorded in 13 healthy subjects during a match-to-sample sensory discrimination task, whereby participants compared the intensity of a thumb-located electric shock (S2) with a prior stimulus to the same location (S1) delivered 8-10s earlier. Stimuli were above or below the individual nociceptive threshold. EEG activity with intracortical source localization via LORETA source reconstruction was analysed during the inter-stimuli period and contrasted with a non-memory-related control task. The inter-stimulus memorization phase was characterized by a focal alpha-activity enhancement, significant during the nociceptive condition only, which progressed from bilateral occipital regions (cuneus and mid-occipital gyri) during the first encoding-memorization phase towards the right-superior and right mid-temporal gyri during the 2-4s immediately preceding S2. Initial alpha enhancement in occipital areas/cuneus is consistent with rapid non-specific inhibition of task-irrelevant visual processing during initial stimulus encoding. Its transfer to the right-temporal regions was concomitant to the temporary upholding of the stimulus perceptual representation, previous to receiving S2, and suggests an active and local blockade of external interferences while these regions actively maintain internal information. These results add to a growing field indicating that alpha oscillations, while indicating local inhibitory processes, can also indirectly reveal active stimulus handling, including maintenance in short-term memory buffers, by objectivizing the filtering out of irrelevant and potentially disrupting inputs in brain regions engaged in internally driven operations.

The role of stimulus periodicity on spinal cord stimulation-induced artificial sensations in rodents

Objective. Sensory feedback is critical for effectively controlling brain-machine interfaces and neuroprosthetic devices. Spinal cord stimulation (SCS) is proposed as a technique to induce artificial sensory perceptions in rodents, monkeys, and humans. However, to realize the full potential of SCS as a sensory neuroprosthetic technology, a better understanding of the effect of SCS pulse train parameter changes on sensory detection and discrimination thresholds is necessary. Approach. Here we investigated whether stimulation periodicity impacts rats’ ability to detect and discriminate SCS-induced perceptions at different frequencies. Main results. By varying the coefficient of variation (CV) of interstimulus pulse interval, we showed that at lower frequencies, rats could detect highly aperiodic SCS pulse trains at lower amplitudes (i.e. decreased detection thresholds). Furthermore, rats learned to discriminate stimuli with subtle differences in periodicity, and the just-noticeable differences from a highly aperiodic stimulus were smaller than those from a periodic stimulus. Significance. These results demonstrate that the temporal structure of an SCS pulse train is an integral parameter for modulating sensory feedback in neuroprosthetic applications.

Influence of reinforcement and its omission on trial-by-trial changes of response bias in perceptual decision making.

Discrimination performance in perceptual choice tasks is known to reflect both sensory discriminability and nonsensory response bias. In the framework of signal detection theory, these aspects of discrimination performance are quantified through separate measures, sensitivity (d') for sensory discriminability and decision criterion (c) for response bias. However, it is unknown how response bias (i.e., criterion) changes at the single-trial level as a consequence of reinforcement history. We subjected rats to a two-stimulus two-response conditional discrimination task with auditory stimuli and induced response bias through unequal reinforcement probabilities for the two responses. We compared three signal-detection-theory-based criterion learning models with respect to their ability to fit experimentally observed fluctuations of response bias on a trial-by-trial level. These models shift the criterion by a fixed step (1) after each reinforced response or (2) after each nonreinforced response or (3) after both. We find that all three models fail to capture essential aspects of the data. Prompted by the observation that steady-state criterion values conformed well to a behavioral model of signal detection based on the generalized matching law, we constructed a trial-based version of this model and find that it provides a superior account of response bias fluctuations under changing reinforcement contingencies.