Disentangling perceptual and response bias in unilateral neglect: a methodological proposal

Bisiach and his colleagues have developed a new version of Milner's "landmark task" for the purpose of separating "perceptual" and "response" biases in neglect patients. Subjects are required to decide which is the longer (or the shorter) of the two portions of a pre-bisected horizontal line. The authors proposed two indices to measure perceptual and response bias respectively. However, these indices are not mathematically independent of one another. Moreover, they do not exploit all of the information available in the data, since they do not consider the effect of the different transection locations across trials. We now propose an alternative means of analyzing data from the revised Landmark task, which generates independent estimates of perceptual and response biases. The method and its theoretical foundation are summarized, and illustrative data obtained from brain damaged patients and control subjects are presented.     

A cueing technique in choice reaction tlme

Much of the fluctuation in choice RT data is assumed to arise from variations in perceptual and response biases correlated with sequential patterns of trial events. Inserting a predictive cue prior to the stimulus on each trial apparently induces a strong bias not only toward that particular stimulus, but also toward its modality and toward the associated response. Trial-to-trial sequential effects under cued conditions were markedly smaller than those obtained in a noncued control condition.     

The dynamics of motivated perception: Effects of control and status on the perception of ambivalent stimuli

Previous studies on attentional biases often show contradictory results. This suggests that important moderating variables have been neglected so far. We suggest that (1) control over potential consequences and (2) satisfaction with the current status are important factors that need to be considered. We explored the influence of these variables using a colour classification task, where colours are associated with financial gains and losses. Data were analysed with hierarchical logistic regression models and with stochastic diffusion models. The latter approach has the special advantage that it allows separating perceptual and judgemental biases. Results show an overall positive judgemental bias. In the absence of control, this positivity bias increases with the amount of money that has been gained, whereas the opposite pattern is present when dangers can be controlled. In the second experiment, no general feedback was given, which led to an increasing negativity bias. Results are discussed within an action theoretic framework.     

Attention improves perceptual quality

Attention has been demonstrated to affect response speed, signal detection, and perceptual enhancement. We wished to determine whether exogenously cued attention had the additional effect of improving the veridicality of perceptual representations. We determined the accuracy and precision of orientation judgments for static and dynamic stimuli when they were, and when they were not, exogenously cued (luminance change). Valid exogenous cues led to more accurate responses that were also quicker. The attentional accuracy benefits were robust to stimulus degradation. Since our task displayed only one test stimulus at a time, response biases cannot account for our results. We concluded that exogenous cues can lead to percepts that are, on average, more similar to the external stimulus. Thus, exogenous cuing can improve perceptual quality.     

Perceptual asymmetries for free viewing of several types of chimeric stimuli.

We examined perceptual biases of right-handers on six free-vision chimeric tasks; two involving a judgement of happiness of a facial expression in photographic and cartoon chimeras, two involving a judgement of femininity in male/female photographic and cartoon chimeras, and two involving a spatial judgement of nonface chimeric stimuli. All four of the face tasks and one of the nonface tasks elicited left spatial field biases of varying magnitudes, and perceptual asymmetries on all tasks were positively correlated. However, multiple correlational analyses revealed that these tests shared differing proportions of variance with each other. Results indicate that, in addition to a common factor or set of factors contributing to lateral biases that is independent of both the nature of the stimulus and whether the stimulus engages lateralized mechanisms, there are distinct lateralized mechanisms which yield different patterns of perceptual asymmetries for different stimuli.     

What kind of bias is hindsight bias?

When people are asked to recollect a former response after having received feedback information, their recollection tends to approach the feedback answer. This phenomenon is referred to as hindsight bias. Recently, Erdfelder and Buchner proposed a multinomial model designed to independently measure the contributions of reconstruction and recollection processes. On its basis, they only found firm evidence for the contribution of reconstruction biases to hindsight effects. In the present study, we tried to experimentally enhance the probability of recollection biases by (a) reducing the depth of processing of the original estimate, (b) minimizing the distinctness of the original estimate and feedback, and (c) combining both treatments. The empirical data were analyzed using a variant of the Erdfelder and Buchner model which allows for the experimental manipulation of the feedback answer. This model is shown to adequately describe the data of our experiment. Moreover, although both treatments were effective in that the first one reduced correct recollections in general and the second one diminished differences between original estimates and recalled estimates, the parameter estimates indicate that the probability of recollecting the original estimate is not hampered by feedback information, even under conditions which are thought to enhance memory impairments. Received: 10 December 1995 / Accepted: 29 October 1997     

Paradoxical cross-over due to attention to high or low spatial frequencies

The mechanisms underlying the right hemisphere's dominance for spatial and attentional functions lacks a comprehensively explanation. For example, perceptual biases, as observed in line bisection and related tasks, might be caused by an attentional asymmetry or by perceptual processes such as a specialization of the left and right hemisphere for high and low spatial frequencies (SFs), respectively. Here we used the gratingscales task to measure perceptual bias in SF judgements, and we cued participants' attention either to high or low SFs. Participants showed a leftward bias when comparing the high SF components of the stimulus, and a rightward bias when comparing the low SF components-opposite to what would be expected from a hemispheric lateralization for SFs. Two control experiments used different strategies to manipulate the width of the attentional window. However, we observed no influence on perceptual bias, thus ruling out the possibility that the results in Experiment 1 were due to differences in attentional window size. These data support the idea of an attentional asymmetry underlying perceptual bias. Our results provide novel support for the role of attentional asymmetry in perceptual biases.     

Breaking the rules in perceptual information integration

We develop a broad theoretical framework for modelling difficult perceptual information integration tasks under different decision rules. The framework allows us to compare coactive architectures, which combine information before it enters the decision process, with parallel architectures, where logical rules combine independent decisions made about each perceptual source. For both architectures we test the novel hypothesis that participants break the decision rules on some trials, making a response based on only one stimulus even though task instructions require them to consider both. Our models take account of not only the decisions made but also the distribution of the time that it takes to make them, providing an account of speed-accuracy tradeoffs and response biases occurring when one response is required more often than another. We also test a second novel hypothesis, that the nature of the decision rule changes the evidence on which choices are based. We apply the models to data from a perceptual integration task with near threshold stimuli under two different decision rules. The coactive architecture was clearly rejected in favor of logical-rules. The logical-rule models were shown to provide an accurate account of all aspects of the data, but only when they allow for response bias and the possibility for subjects to break those rules. We discuss how our framework can be applied more broadly, and its relationship to Townsend and Nozawa’s (1995) Systems-Factorial Technology.     

The differential outcomes procedure can overcome self-bias in perceptual matching

There are biases in perceptual matching between shapes and labels referring to familiar others, compared with when the labels refer to unfamiliar people. We assessed whether these biases could be affected by differential feedback (using the differential outcomes procedure [DOP]) compared with when feedback is provided using a nondifferential outcomes procedure (NOP). Participants formed associations between simple geometric shapes and labels referring to people the participant did or did not know (self, best friend, other). Subsequently, the task was to match a label to one of two shapes shown on a trial. When feedback for correct responses was given following the NOP condition, matches were faster to known people (self and friend) compared with those to an unknown person (stranger). However, this advantage for known personal relations was eliminated when participants were given feedback for correct responses following the DOP condition. The data are consistent with prior work showing that the DOP can facilitate the learning of taxing associations (for the stranger stimuli relative to the familiar self and friend stimuli). In addition, the results suggest that the facilitated perceptual matching for stimuli associated to individuals known personally may reflect better individuation of the association between the shape stimulus and the label, a process enhanced by using a DOP for associations with unfamiliar people.     

Visual nesting of stimuli affects rhesus monkeys’ (Macaca mulatta) quantity judgments in a bisection task

Nonhuman animals are highly proficient at judging relative quantities presented in a variety of formats, including visual, auditory, and even cross-modal formats. Performance typically is constrained by the ratio between sets, as would be expected under Weber’s law and as is described in the approximate number system (ANS) hypothesis. In most cases, tests are designed to avoid any perceptual confusion for animals regarding the stimulus sets, but despite this, animals show some of the perceptual biases that humans show based on organization of stimuli. Here, we demonstrate an additional perceptual bias that emerges from the illusion of nested sets. When arrays of circles were presented on a computer screen and were to be classified as larger than or smaller than an established central value, rhesus monkeys (Macaca mulatta) underestimated quantities when circles were nested within each other. This matched a previous report with adult humans (Chesney & Gelman, Attention, Perception, & Psychophysics 24:1104–1113, 2012), indicating that macaques, like humans, show the pattern of biased perception predicted by ANS estimation. Although some macaques overcame this perceptual bias, demonstrating that they could come to view nested stimuli as individual elements to be included in the estimates of quantity used for classifying arrays, the majority of the monkeys showed the bias of underestimating nested arrays throughout the experiment.     

Evidence against response bias in temporal order tasks with attention manipulation by masked primes

Attending to a location shortens the perceptual latency of stimuli appearing at this location (perceptual latency priming). According to attentional explanations, perceptual latency priming relies on the speeded transfer of attended visual information into an internal model. However, doubts about the attentional origin have repeatedly been raised because efforts to minimize response bias have been insufficient in most studies. Five experiments investigated the contribution of a response bias to perceptual latency priming (judgment bias due to the two-alternative forced-choice method and due to the existence of the prime, criterion effects or second-order bias, sensorimotor priming). If any, only small response biases were found. The results thus support the attentional explanation.     

Feedback versus an illusion in time

The accuracy of many perceptual comparisons depends greatly on the order in which the to-be-compared stimuli are presented. With comparisons of durations around 300 ms, these presentation-order effects do not diminish, even with extended practice, when feedback about response accuracy is withheld. Providing such feedback greatly diminishes presentation-order effects and coincidentally produces substantial increases in response accuracy. The feedback acts in part through inducing response biases and in part through changes in sensitivity. The contradiction between studies which report time-order errors in duration comparison and those which do not is attributable to differences in the use of information feedback.     

Affective state influences perception by affecting decision parameters underlying bias and sensitivity

Studies of the effect of affect on perception often show consistent directional effects of a person's affective state on perception. Unpleasant emotions have been associated with a "locally focused" style of stimulus evaluation, and positive emotions with a "globally focused" style. Typically, however, studies of affect and perception have not been conducted under the conditions of perceptual uncertainty and behavioral risk inherent to perceptual judgments outside the laboratory. We investigated the influence of perceivers' experienced affect (valence and arousal) on the utility of social threat perception by combining signal detection theory and behavioral economics. We compared 3 perceptual decision environments that systematically differed with respect to factors that underlie uncertainty and risk: the base rate of threat, the costs of incorrect identification threat, and the perceptual similarity of threats and nonthreats. We found that no single affective state yielded the best performance on the threat perception task across the 3 environments. Unpleasant valence promoted calibration of response bias to base rate and costs, high arousal promoted calibration of perceptual sensitivity to perceptual similarity, and low arousal was associated with an optimal adjustment of bias to sensitivity. However, the strength of these associations was conditional upon the difficulty of attaining optimal bias and high sensitivity, such that the effect of the perceiver's affective state on perception differed with the cause and/or level of uncertainty and risk.     

反馈延迟与掩蔽类型对知觉类别学习的影响

通过两个实验探讨反馈延迟与掩蔽类型对知觉类别学习的影响。实验1光栅掩蔽条件下,采用2（类别结构：基于规则vs.信息整合）×2（延迟反馈：500vs.3000ms）被试间实验设计,实验2采用同样的实验设计,保持延迟反馈时间不变,但改掩蔽类型为黑屏掩蔽。结果发现：（1）光栅掩蔽条件下,反馈延迟削弱信息整合类别结构的成绩,不影响基于规则类别学习,内隐外显类别结构之间存在分离效应。（2）黑屏掩蔽条件下,信息整合与基于规则类别结构的成绩均不受到延迟反馈的影响,分离效应消失。实验说明“无关因素”掩蔽影响知觉类别学习,知觉噪音与标准噪音在反馈延迟影响知觉类别学习中起到重要作用,COVIS模型理论关于延迟反馈时间影响知觉类别学习的解释具有局限性。     

Observational drawing biases are predicted by biases in perception: Empirical support of the misperception hypothesis of drawing accuracy with respect to two angle illusions

We tested the misperception hypothesis of drawing errors, which states that drawing accuracy is strongly influenced by the perceptual encoding of a to-be-drawn stimulus. We used a highly controlled experimental paradigm in which nonartist participants made perceptual judgements and drawings of angles under identical stimulus exposure conditions. Experiment 1 examined the isosceles/scalene triangle angle illusion; congruent patterns of bias in the perception and drawing tasks were found for 40 and 60° angles, but not for 20 or 80° angles, providing mixed support for the misperception hypothesis. Experiment 2 examined shape constancy effects with respect to reproductions of single acute or obtuse angles; congruent patterns of bias in the perception and drawing tasks were found across a range of angles from 29 to 151°, providing strong support for the misperception hypothesis. In both experiments, perceptual and drawing biases were positively correlated. These results are largely consistent with the misperception hypothesis, suggesting that inaccurate perceptual encoding of angles is an important reason that nonartists err in drawing angles from observation.     

Unilateral hemispheric activation does not affect free-viewing perceptual asymmetries

Strong leftward perceptual biases have been reported for the selection of the darker of two left/right mirror-reversed luminance gradients under free-viewing conditions. This study investigated the effect of unilateral hemispheric activation on this leftward bias in two groups of dextrals (N = 52 and N = 24). In Experiment 1, activation was manipulated by asking participants to tap with their left or right fingers along their midline. In Experiment 2, participants clenched their left or right hands in their respective hemispaces. Participants selected the stimulus that was darker on the left-hand side 73% of the time. Despite manipulations of activation strength and hemispace, activation had no effect on the asymmetry. If activation was important, the leftward bias should have been enhanced when the left hand/right hemisphere was active and reduced (or reversed) when the right hand/left hemisphere was active. The contribution of left-to-right scanning biases to free-viewing perceptual asymmetries is discussed as an alternative.     

Global and local processing in Williams syndrome: drawing versus perceiving.

It has been hypothesized that a local processing bias underlies overall visuospatial impairments in Williams syndrome (WS). However, recent studies have challenged this hypothesis by providing evidence against a local processing bias at the perceptual level. The aim of the present study was to further examine drawing and perceptual skills in children with WS using closely matched-hierarchical stimuli. In the drawing task children with WS exhibited a local processing bias. However, no significant preferential bias was found in the perceptual task. This indicates that children with WS do not systematically present a preferential bias for local information. Taken together the findings of the present study suggest that perceptual processing deficits per se are unlikely to explain local processing biases in visuoconstructive tasks often described in people with WS.     

Global and Local processing in Williams Syndrome: Drawing versus Perceiving

It has been hypothesized that a local processing bias underlies overall visuospatial impairments in Williams syndrome (WS). However, recent studies have challenged this hypothesis by providing evidence against a local processing bias at the perceptual level. The aim of the present study was to further examine drawing and perceptual skills in children with WS using closely matched-hierarchical stimuli. In the drawing task children with WS exhibited a local processing bias. However, no significant preferential bias was found in the perceptual task. This indicates that children with WS do not systematically present a preferential bias for local information. Taken together the findings of the present study suggest that perceptual processing deficits per se are unlikely to explain local processing biases in visuoconstructive tasks often described in people with WS.     

Recency effects as a window to generalization: separating decisional and perceptual sequential effects in category learning

Accounts of learning and generalization typically focus on factors related to lasting changes in representation (i.e., long-term memory). The authors present evidence that shorter term effects also play a critical role in determining performance and that these recency effects can be subdivided into perceptual and decisional components. Experimental results based on a probabilistic category structure show that the previous stimulus exerts a contrastive effect on the current percept (perceptual recency) and that responses are biased toward or away from the previous feedback, depending on the similarity between successive stimuli (decisional recency). A method for assessing these recency effects is presented that clarifies open questions regarding stimulus generalization and perceptual contrast effects in categorization and in other domains.     

Perceptual and cognitive biases in individuals with body dysmorphic disorder symptoms

Given the extreme focus on perceived physical defects in body dysmorphic disorder (BDD), we expected that perceptual and cognitive biases related to physical appearance would be associated with BDD symptomology. To examine these hypotheses, participants (N=70) high and low in BDD symptoms completed tasks assessing visual perception and cognition. As expected, there were significant group differences in self-relevant, but not other-relevant, cognitive biases. Perceptual bias results were mixed, with some evidence indicating that individuals high (versus low) in BDD symptoms literally see themselves in a less positive light. Further, individuals high in BDD symptoms failed to demonstrate a normative self-enhancement bias. Overall, this research points to the importance of assessing both cognitive and perceptual biases associated with BDD symptoms, and suggests that visual perception may be influenced by non-visual factors.