Response Bias Reflects Individual Differences in Sensory Encoding

What is the topic of this review? In 'personalized medicine', various plots and analyses are purported to quantify individual differences in intervention response, identify responders/non-responders and explore response moderators or mediators. What advances does it highlight? We highlight the impact of within-subject random variation, which is inevitable even with 'gold-standard' measurement tools/protocols and sometimes so substantial that it explains all apparent individual response differences. True individual response differences are quantified only by comparing the SDs of changes between intervention and comparator arms. When these SDs are similar, true individual response differences are clinically unimportant and further analysis unwarranted. Within the 'hot topic' of personalized medicine, we scrutinize common approaches for presenting and quantifying individual differences in the physiological response to an intervention. First, we explain how popular plots used to present individual differences in response are contaminated by random within-subject variation and the regression to the mean artefact. Using a simulated data set of blood pressure measurements, we show that large individual differences in physiological response can be suggested by some plots and analyses, even when the true magnitude of response is exactly the same in all individuals. Second, we present the appropriate designs and analysis approaches for quantifying the true interindividual variation in physiological response. It is imperative to include a comparator arm/condition (or derive information from a prior relevant repeatability study) to quantify true interindividual differences in response. The most important statistic is the SD of changes in the intervention arm, which should be compared with the same SD in the comparator arm or from a prior repeatability study in the same population conducted over the same duration as the particular intervention. Only if the difference between these SDs is clinically relevant is it logical to go on to explore any moderators or mediators of the intervention effect that might explain the individual response. To date, very few researchers have compared these SDs before making claims about individual differences in physiological response and their importance to personalized medicine.

Previous studies have brought conflicting results regarding the effects of valence and arousal in visual word processing. Some authors have pointed to participants’ individual differences as one of the possible explanations for these inconsistencies. The main aim of the present research was to examine whether participants’ individual differences in the level of epistemically unwarranted beliefs (EUB) contribute to these conflicting results. Therefore, participants who varied in their level of paranormal, pseudoscientific and conspiracy beliefs (assessed by self-report measures) performed a lexical decision task (LDT) and a recognition memory task. Linear mixed-effects models over LDT response times revealed that the effects of words’ emotional content (both valence and arousal) were modulated by the degree of individuals’ EUB. In addition, signal detection theory analyses showed that in the recognition task (but not in the LDT) response bias became more liberal as individuals’ EUB increased. These patterns of effects were not general to all EUB instances. The obtained results highlight the need to consider participants’ individual differences in affective word processing and signal detection. In addition, this study reveals some basic psychological mechanisms that would underlie EUB, a fact that has both theoretical and applied relevance.

Can humans discriminate between healthy and sick individuals, and if so by what cues? In order to study these important questions, in a recent study, Axelsson et al . let 62 untrained raters decide for 32 facial photos whether the person in the photo was healthy or sick [1]. Photos were taken of 16 healthy volunteers, injected once with a lipopolysaccharide injection ( Escherichia coli endotoxin) and once with a placebo injection (with a three to four week interval in between). Photos were taken 2 h after injection. While the authors used this ingenious study design to estimate the average discrimination ability of raters, their analysis did not address two keys aspects pertaining to their research questions. First, they did not report whether and how individuals differ in discrimination ability. Individuals may differ in their ability to discriminate between healthy and sick individuals, and in how they balance the trade-off between sensitivity (i.e. the frequency of sick individuals classified as sick) and specificity (i.e. the frequency of healthy individuals classified as healthy), a.k.a. response bias [2]. Importantly, while the authors did not use their data to investigate the presence and structure of such differences, the implications of their work for disease dynamics—and consequently prevention strategies—will differ substantially between populations with and without individual differences [3–5]. For example, groups and populations with a large number of expert and/or ‘cautious’ individuals (i.e. individuals with a relatively low response bias) are predicted to have a lower prevalence and weaker infectious outbreaks than groups with fewer expert and/or cautious individuals. Second, while the authors investigated the discrimination ability of socially isolated raters, in many real-world contexts, individuals will be able to observe the responses of others to potentially sick individuals. In such situations, the social information present …

"Normal hearing" is typically defined by threshold audibility, even though everyday communication relies on extracting key features of easily audible sound, not on sound detection. Anecdotally, many normal-hearing listeners report difficulty communicating in settings where there are competing sound sources, but the reasons for such difficulties are debated: Do these difficulties originate from deficits in cognitive processing, or differences in peripheral, sensory encoding? Here we show that listeners with clinically normal thresholds exhibit very large individual differences on a task requiring them to focus spatial selective auditory attention to understand one speech stream when there are similar, competing speech streams coming from other directions. These individual differences in selective auditory attention ability are unrelated to age, reading span (a measure of cognitive function), and minor differences in absolute hearing threshold; however, selective attention ability correlates with the ability to detect simple frequency modulation in a clearly audible tone. Importantly, we also find that selective attention performance correlates with physiological measures of how well the periodic, temporal structure of sounds above the threshold of audibility are encoded in early, subcortical portions of the auditory pathway. These results suggest that the fidelity of early sensory encoding of the temporal structure in suprathreshold sounds influences the ability to communicate in challenging settings. Tests like these may help tease apart how peripheral and central deficits contribute to communication impairments, ultimately leading to new approaches to combat the social isolation that often ensues.

If emotions guide consciousness, people may recognize degraded objects in center view more accurately if they either fear the objects or are disgusted by them. Therefore, we studied whether recognition of spiders and snakes correlates with individual differences in spider fear, snake fear, and disgust sensitivity. Female students performed a recognition task with pictures of spiders, snakes, flowers, and mushrooms as well as blanks. Pictures were backward masked to reduce picture visibility. Signal detection analyses showed that recognition of spiders and snakes was correlated with disgust sensitivity but not with fear of spiders or snakes. Further, spider fear correlated with the tendency to misinterpret blanks as threatening (response bias). These findings suggest that effects on recognition and response biases to emotional pictures vary for different emotions and emotional traits. Whereas fear may induce response biases, disgust may facilitate recognition.

Structure of visual biases revealed by individual differences

The identification and discrimination of vowel duration was investigated. The experimental results could not be unambiguously interpreted in favour of either categorial or continuous perception of the acoustic variable under study. Furthermore, the subjects' response bias in the discrimination test was examined. It turned out that the number of "false alarms" (i.e. "different" responses to pairs of physically identical stimuli) varied in a systematic manner, being considerably higher near the phoneme boundary (as established by identification tests) than within the phoneme areas. It is attempted to explain the systematic variation of response bias in terms of Fujisaki and Kawashima's model of the decision process in discrimination tasks.

The internal representation of stimuli is imperfect and subject to bias. Noise introduced at initial encoding and during maintenance degrades the precision of representation. Stimulus estimation is also biased away from recently encountered stimuli, a phenomenon known as adaptation. Within a Bayesian framework, greater biases are predicted to result from poor precision. We tested for this effect on individual difference measures. Through an online experiment, 202 subjects contributed data. During separate face and color blocks, they performed three different tasks: an immediate stimulus match, a delayed match-to-sample, and a delayed match following 5 s of adaptation. The stimulus spaces were circular, and subjects entered their responses on a color/face wheel. Bias and precision of responses were extracted while accounting for the probability of random guesses. We found that the adaptation manipulation induced the expected bias in responses, and the magnitude of this bias varied reliably and substantially between subjects. Across subjects, there was a negative correlation between mean precision and bias. This relationship was replicated in a new experiment with 192 subjects. This result is consistent with a Bayesian observer model, in which the precision of perceptual representation influences the magnitude of perceptual bias.

According to signal detection theory, old-new recognition decisions can be affected by response bias, a general proclivity to respond either "old" or "new." In recognition experiments, response bias is usually analyzed at a group level, but substantial individual differences in bias can underlie group means. These differences suggest that, independent of any experimental manipulation, some people require more memory evidence than do others before they are willing to call an item "old." In four experiments, we investigated the possibility that recognition response bias is a partial function of a trait-like predisposition. Bias was highly correlated across two recognition study-test cycles separated by 10 min (Experiment 1). A nearly identical correlation was observed when the tasks were separated by one week (Experiment 2). Bias correlations remained significant even when the stimuli differed sharply between the first and second study-test cycles (Experiment 3). No relationship was detected between bias and response strategies in two general knowledge tests (Experiments 2 and 4), but bias did weakly predict frequency of false recall in the Deese/Roediger-McDermott (DRM) paradigm (Experiment 4). This evidence of trait-like stability suggests an entirely different aspect of response bias than that studied by examining its modulation by task variables, one for which complete theories of recognition memory may need to account.

Among-individual variation in performance on cognitive tasks is ubiquitous across species that have been examined, and understanding the evolution of cognitive abilities requires investigating among-individual variation because natural selection acts on individual differences. However, relatively little is known about the extent to which individual differences in cognition are determined by domain-specific compared with domain-general cognitive abilities. We examined individual differences in learning speed of zebra finches across seven different tasks to determine the extent of domain-specific versus domain-general learning abilities, as well as the relationship between learning speed and learning generalization. Thirty-two zebra finches completed a foraging board experiment that included visual and structural discriminations, and then these same birds went through an acoustic operant discrimination experiment that required discriminating between different natural categories of acoustic stimuli. We found evidence of domain-general learning abilities as birds’ relative performance on the seven learning tasks was weakly repeatable and a principal components analysis found a first principal component that explained 36% of the variance in performance across tasks with all tasks loading unidirectionally on this component. However, the few significant correlations between tasks and high repeatability within each experiment suggest the potential for domain-specific abilities. Learning speed did not influence an individual’s ability to generalize learning. These results suggest that zebra finch performance across visual, structural, and auditory learning relies upon some common mechanism; some might call this evidence of “general intelligence”(g), but it is also possible that this finding is due to other noncognitive mechanisms such as motivation.Supplementary InformationThe online version contains supplementary material available at 10.3758/s13420-022-00520-w.

An imbalance between top-down and bottom-up processing on perception (specifically, over-reliance on top-down processing) can lead to anomalous perception, such as illusions. One factor that may be involved in anomalous perception is visual mental imagery, which is the experience of “seeing” with the mind’s eye. There are vast individual differences in self-reported imagery vividness, and more vivid imagery is linked to a more sensory-like experience. We, therefore, hypothesized that susceptibility to anomalous perception is linked to individual imagery vividness. To investigate this, we adopted a paradigm that is known to elicit the perception of faces in pure visual noise (pareidolia). In four experiments, we explored how imagery vividness contributes to this experience under different response instructions and environments. We found strong evidence that people with more vivid imagery were more likely to see faces in the noise, although removing suggestive instructions weakened this relationship. Analyses from the first two experiments led us to explore confidence as another factor in pareidolia proneness. We, therefore, modulated environment noise and added a confidence rating in a novel design. We found strong evidence that pareidolia proneness is correlated with uncertainty about real percepts. Decreasing perceptual ambiguity abolished the relationship between pareidolia proneness and both imagery vividness and confidence. The results cannot be explained by incidental face-like patterns in the noise, individual variations in response bias, perceptual sensitivity, subjective perceptual thresholds, viewing distance, testing environments, motivation, gender, or prosopagnosia. This indicates a critical role of mental imagery vividness and perceptual uncertainty in anomalous perceptual experience.

Students with intellectual disabilities (IDs) have various learning difficulties and are at risk for school failure. Large inter-individual differences are described for reading, but it is unclear how these vary as a function of grade. The aim of this study was to examine various reading fluency, accuracy and comprehension parameters in second-to-eighth-grade Italian children with either borderline intellectual functioning (BIF) or mild ID (MID). We examined 106 children with BIF (67 M and 39 F) and 168 children with MID (107 M and 61 F). The children were in the second to eighth grade and were comparable for chronological age (7 to 14years). They were administered a battery of tests that assessed fluency and accuracy of word, pseudo-word and text reading, as well as text comprehension. Standardised scores allowed us to compare the performance of the two groups with normative values. Children with ID obtained generally low scores compared with normative values. Those with MID had greater difficulty than those with BIF. Furthermore, difficulty was greater for speed than for accuracy measures and for words than for pseudo-words. Difficulty (particularly in the case of reading speed) tended to be pronounced at later grades. Marked individual differences were present independently of MID-BIF subgrouping, as well as stimulus category and reading parameter. As a group, children with ID showed difficulty in reading acquisition; the effect was greater for children with more severe ID, but large individual differences were observed in children with both BIF and MID. Relatively spared pseudo-word reading skills indicate efficient use of the grapheme-to-phoneme conversion routine. This processing mode may prove more ineffective at higher levels of schooling when even in regular orthographies such as Italian typically developing children rely on lexical activation.

Past research on gender-related brain asymmetries in emotions was limited and not univocal. The present study analyzed EEG alpha activity (indexing cortical de-activation) from 64 scalp sites in 20 women and 20 men during a counterbalanced block presentation of emotional slides and short video-clips. Stimuli consisted of 45 brief clips of 13 s, divided into 15 erotic (pleasant), 15 neutral and 15 fear (unpleasant) contents. Slides consisted in 45 photo shots (presented for 13 s each) extracted from the videos. As expected, women perceived fear stimuli as more arousing and more unpleasant compared to men. Alpha EEG source analysis revealed gender effects depending on stimulus. Emotional film-clips elicited in both groups a pattern of greater right than left occipital activation. Instead, emotional pictures activated opposite occipital regions, as women showed greater activation in the left, men in the right hemisphere. Men also showed greater activation to Erotic compared to Fear stimuli (i.e., pictures/clips) in the posterior parietal complex. Results point to the relevance of emotional stimulus type to reveal gender effects: clips are ecological, dynamic and engaging, and forced a unified pattern of emotional responses that reset individual differences. Emotional pictures, less engaging, allowed individual differences to emerge and interact with the stimulus category.

Processing of prosodic phrasing requires listeners to integrate acoustic cues that unfold incrementally during speech comprehension, yet substantial individual differences exist in how listeners use unfolding prosodic information. This study investigated whether individual differences in auditory-perceptual discrimination abilities for prosodic boundary cues are related to processing of prosodic phrasing, and, more specifically, the ability to use the incremental bottom-up prosodic information for making top-down predictions about the syntactic structure of an unfolding utterance. Sixty German-speaking adults completed adaptive staircase procedures measuring Just-Noticeable-Difference thresholds for auditory-perceptual acuity in pitch, pause, and final lengthening discrimination. In addition, they performed a gating task that provided snippets of coordinate three-name sequences with or without an internal prosodic boundary in a randomized order. Performance in the gating task was analyzed using Bayesian multilevel Signal Detection Theory models to separate discriminability from response bias. Participants with higher auditory-perceptual acuity demonstrated better prediction of the upcoming structure across all gates. When all three auditory-perceptual acuity measures were modeled simultaneously, each individual effect attenuated substantially, indicating shared, rather than independent, predictive variance. These findings suggest that top-down prediction during speech comprehension is related to overall auditory-perceptual acuity rather than independent boundary-cue-specific sensitivities.

Twenty subject response parameters, including scales to measure re- sponse reliability, content and acquiescence variance, social desirability, yea- and nay-saying, and extremeness response style were obtained for 88 college students, based on 89 pairs of adjecCives oppoSrite both in content and in social desirability. Test-retest item reversal methodology was used to evaluate the possible effects of these biases on responses to the trait-descriptive adjectives. Individual differences in response bias propensities were studied among the various subject response parameters, and in relation to scale scores from the 16 PF, MMPI, and CPI. The results supported a content rather than bias interpretation of the subjects' selfdescriptions for the adjectives. Additionally, no useful associations were found between measures of personality characteristics and response biases.