What makes a stimulus worthy of attention: Cue-outcome correlation and choice relevance in the learned predictiveness effect

The learned predictiveness effect refers to the tendency for predictive cues to attract greater attention and show faster learning in subsequent tasks. However, in typical designs, the predictiveness of each cue (its objective cue-outcome correlation) is confounded with the degree to which it is informative for making the correct response on each trial (a feature we term choice relevance). In four experiments, we tested the unique contributions of cue-outcome correlation and choice relevance to the learned predictiveness effect by manipulating the outcome choices available on each trial. Experiments 1A and 1B compared two sets of partially predictive cues and found that participants learned more in a transfer phase about the set of cues that were previously choice-relevant. Experiments 2A and 2B used a design in which the cue-outcome correlation was stronger for one set of cues (perfect predictors) than the other set (imperfect predictors). Manipulating the choice relevance of the imperfect predictors in this design did not influence the magnitude of the learning bias toward the perfect predictor. Unlike cue-outcome correlation, choice relevance did not seem to correspond to biases in eye-gaze, suggesting that it operates via a distinct mechanism. Simulations with a modified EXIT model successfully predicted cue-outcome correlation and choice relevance effects by assuming that participants update learning for present outcomes only, but incorrectly predicted additive effects. We conclude that cue-outcome correlation and choice relevance are important factors that can lead to biases in future learning; both were individually sufficient but neither was necessary. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A disease-associated gene desert directs macrophage inflammation through ETS2

Increasing rates of autoimmune and inflammatory disease present a burgeoning threat to human health1. This is compounded by the limited efficacy of available treatments1 and high failure rates during drug development2, highlighting an urgent need to better understand disease mechanisms. Here we show how functional genomics could address this challenge. By investigating an intergenic haplotype on chr21q22-which has been independently linked to inflammatory bowel disease, ankylosing spondylitis, primary sclerosing cholangitis and Takayasu's arteritis3-6-we identify that the causal gene, ETS2, is a central regulator of human inflammatory macrophages and delineate the shared disease mechanism that amplifies ETS2 expression. Genes regulated by ETS2 were prominently expressed in diseased tissues and more enriched for inflammatory bowel disease GWAS hits than most previously described pathways. Overexpressing ETS2 in resting macrophages reproduced the inflammatory state observed in chr21q22-associated diseases, with upregulation of multiple drug targets, including TNF and IL-23. Using a database of cellular signatures7, we identified drugs that might modulate this pathway and validated the potent anti-inflammatory activity of one class of small molecules in vitro and ex vivo. Together, this illustrates the power of functional genomics, applied directly in primary human cells, to identify immune-mediated disease mechanisms and potential therapeutic opportunities.

ACAD9 treatment with bezafibrate and nicotinamide riboside temporarily stabilizes cardiomyopathy and lactic acidosis

Pathogenic ACAD9 variants cause complex I deficiency. Patients presenting in infancy unresponsive to riboflavin have high mortality. A six-month-old infant presented with riboflavin unresponsive lactic acidosis and life-threatening cardiomyopathy. Treatment with high dose bezafibrate and nicotinamide riboside resulted in marked clinical improvement including reduced lactate and NT-pro-brain type natriuretic peptide levels, with stabilized echocardiographic measures. After a long stable period, the child succumbed from cardiac failure with infection at 10.5 months. Therapy was well tolerated. Peak bezafibrate levels exceeded its EC50. The clinical improvement with this treatment illustrates its potential, but weak PPAR agonist activity of bezafibrate limited its efficacy.

The role of uncertainty in regulating associative change

Rescorla (2000, 2001) interpreted his compound test results to show that both common and individual error terms regulate associative change such that the element of a conditioned compound with the greater prediction error undergoes greater associative change than the one with the smaller prediction error. However, it has recently been suggested that uncertainty, not prediction error, is the primary determinant of associative change in people (Spicer et al., 2020, 2022). The current experiments use the compound test in a continuous outcome allergist task to assess the role of uncertainty in associative change, using two different manipulations of uncertainty: outcome uncertainty (where participants are uncertain of the level of the outcome on a particular trial) and causal uncertainty (where participants are uncertain of the contribution of the cue to the level of the outcome). We replicate Rescorla's compound test results in the case of both associative gains (Experiment 1) and associative losses (Experiment 3) and then provide evidence for greater change to more uncertain cues in the case of associative gains (Experiments 2 and 4), but not associative losses (Experiments 3 and 5). We discuss the findings in terms of the notion of theory protection advanced by Spicer et al., and other ways of thinking about the compound test procedure, such as that proposed by Holmes et al. (2019). (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Unidirectional rating scales overestimate the illusory causation phenomenon

Illusory causation is a phenomenon in which people mistakenly perceive a causal relationship between a cue and outcome even though the contingency between them is actually zero. Illusory causation studies typically use a unidirectional causal rating scale, where one endpoint refers to no relationship and the other to a strongly positive causal relationship. This procedure may bias mean causal ratings in a positive direction, either by censoring negative ratings or by discouraging participants from giving the normative rating of zero which is at the bottom extreme of the scale. To test this possibility, we ran two experiments that directly compared the magnitude of causal illusions when assessed with a unidirectional (zero-positive) versus a bidirectional (negative-zero-positive) rating scale. Experiment 1 used high cue and outcome densities (both 75%), whereas Experiment 2 used neutral cue and outcome densities (both 50%). Across both experiments, we observed a larger illusory causation effect in the unidirectional group compared with the bidirectional group, despite both groups experiencing the same training trials. The causal illusions in Experiment 2 were observed despite participants accurately learning the conditional probabilities of the outcome occurring in both the presence and absence of the cue, suggesting that the illusion is driven by the inability to accurately integrate conditional probabilities to infer causal relationships. Our results indicate that although illusory causation is a genuine phenomenon that is observable with either a undirectional or a bidirectional rating scale, its magnitude may be overestimated when unidirectional rating scales are used.

Using unobserved causes to explain unexpected outcomes: The effect of existing causal knowledge on protection from extinction by a hidden cause

People often rely on the covariation between events to infer causality. However, covariation between cues and outcomes may change over time. In the associative learning literature, extinction provides a model to study updating of causal beliefs when a previously established relationship no longer holds. Prediction error theories can explain both extinction and protection from extinction when an inhibitory (preventive) cue is present during extinction. In three experiments using the allergist causal learning task, we found that protection could also be achieved by a hidden cause that was inferred but not physically present, so long as that cause was a plausible preventer of the outcome. We additionally showed complete protection by a physically presented cue that was neutral rather than inhibitory at the outset of extinction. Both findings are difficult to reconcile with dominant prediction error theories. However, they are compatible with the idea of theory protection, where the learner attributes the absence of the outcome to the added cue (when present) or to a hidden cause, and therefore does not need to revise causal beliefs about A. Our results suggest that prediction error encourages changes in causal beliefs, but the nature of the change is determined by reasoning processes that incorporate existing knowledge of causal mechanisms and may be biased toward preservation of existing beliefs. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

A cognitive pathway to punishment insensitivity

Individuals differ in their sensitivity to the adverse consequences of their actions, leading some to persist in maladaptive behaviors. Two pathways have been identified for this insensitivity: a motivational pathway based on excessive reward valuation and a behavioral pathway based on autonomous stimulus-response mechanisms. Here, we identify a third, cognitive pathway based on differences in punishment knowledge and use of that knowledge to suppress behavior. We show that distinct phenotypes of punishment sensitivity emerge from differences in what people learn about their actions. Exposed to identical punishment contingencies, some people (sensitive phenotype) form correct causal beliefs that they use to guide their behavior, successfully obtaining rewards and avoiding punishment, whereas others form incorrect but internally coherent causal beliefs that lead them to earn punishment they do not like. Incorrect causal beliefs were not inherently problematic because we show that many individuals benefit from information about why they are being punished, revaluing their actions and changing their behavior to avoid further punishment (unaware phenotype). However, one condition where incorrect causal beliefs were problematic was when punishment is infrequent. Under this condition, more individuals show punishment insensitivity and detrimental patterns of behavior that resist experience and information-driven updating, even when punishment is severe (compulsive phenotype). For these individuals, rare punishment acted as a "trap," inoculating maladaptive behavioral preferences against cognitive and behavioral updating.

Retardation of acquisition after conditioned inhibition and latent inhibition training in human causal learning

Inhibitory stimuli are slow to acquire excitatory properties when paired with the outcome in a retardation test. However, this pattern is also seen after simple nonreinforced exposure: latent inhibition. It is commonly assumed that retardation would be stronger for a conditioned inhibitor than for a latent inhibitor, but there is surprisingly little empirical evidence comparing the two in either animals or humans. Thus, retardation after inhibitory training could in principle be attributable entirely to latent inhibition. We directly compared the speed of excitatory acquisition after conditioned inhibition and matched latent inhibition training in human causal learning. Conditioned inhibition training produced stronger transfer in a summation test, but the two conditions did not differ substantially in a retardation test. We offer two explanations for this dissociation. One is that learned predictiveness attenuated the latent inhibition that otherwise would have occurred during conditioned inhibition training, so that retardation in that condition was primarily due to inhibition. The second explanation is that inhibitory learning in these experiments was hierarchical in nature, similar to negative occasion-setting. By this account, the conditioned inhibitor was able to negatively modulate the test excitor in a summation test, but was no more retarded than a latent inhibitor in its ability to form a direct association with the outcome. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Reduction in caffeine withdrawal after open-label decaffeinated coffee

BACKGROUND

Withdrawal from addictive drugs can be reduced by administering placebo deceptively, but in the clinic it is unethical to deceive the patient. Open-label placebo effects have been observed across a range of psychophysiological phenomena, and may also apply to drug withdrawal.

METHOD

24-hour abstinent heavy coffee drinkers (N = 61) rated their caffeine withdrawal symptoms before being allocated to one of three groups. The Deceptive group was given decaffeinated coffee (decaf) and told it was caffeinated, the Open-Label group given decaf and told it was decaf and the Control group given water and told it was water. After 45 min, caffeine withdrawal was measured again. All participants rated their expectancies of withdrawal reduction from caffeinated coffee, decaf and water prior to being randomised and the end of the study.

RESULTS

There was a significant 9.5-point reduction in caffeine withdrawal in the Open-Label group (95% confidence interval (CI): 4.7, 14.3; p = 0.002), which was 8.6 points less than the Deceptive group (95%CI: 0.4, 16.8; p = 0.014) but 8.9 points greater than the Control group (95%CI: 0.6, 17.2; p = 0.012). Pre-randomisation, participants expected caffeinated coffee to reduce their withdrawal symptoms the most, followed by water and decaf, Pre-randomisation expectancy of withdrawal was only associated with amount of withdrawal reduction in the Deceptive group.

CONCLUSION

It appears as if open-label placebo caffeine (i.e. decaf) can reduce caffeine withdrawal symptoms, even when people do not hold a conscious expectancy it will do so. There may be ways to integrate open-label placebo procedures into clinical interventions for drug dependence without violating informed consent.

Surgical challenges of giant parathyroid adenomas weighing 10 g or more

PURPOSE

An average parathyroid adenoma (PA) weighs < 1 g. This study aimed to characterise giant PAs ≥ 10 g (GPAs) to facilitate surgical management of primary hyperparathyroidism (PHPT).

METHODS

All patients with a GPA confirmed on histology were recruited from the Monash University Endocrine Surgery Unit database. Clinical and demographic data were collected and compared to a group of non-GPA patients.

RESULTS

A total of 14 GPAs were identified between 2007 and 2018 out of 863 patients (1.6%) with a single PA excised for PHPT. The GPA patients were compared to a control group of 849 non-GPA patients in the same period with similar mean age (62 ± 16 vs 63 ± 14, P = 0.66) and gender distribution (64% vs 75% female, P = 0.35). Pre-operative calcium (Ca) and parathyroid hormone (PTH) levels were significantly higher in GPA patients (P < 0.001). A higher percentage of GPA patients (79%) had concordant localisation studies (ultrasound and sestamibi) than control patients (59%), (P = 0.13), but they were significantly less likely to undergo MIP (55% vs 82%, P = 0.02). The median GPA weighed 12.5 g (IQR 10.5-24.3). Median serum Ca normalised by day 1 post-operatively, while PTH remained elevated. Both serum Ca and PTH levels were in the normal range at 3 months. All GPA lesions were benign on histopathology.

CONCLUSION

GPAs are rare and display severe clinical and biochemical abnormalities. Despite their large size, concordant pre-operative imaging was not always achieved, and a few patients were suitable for MIP.

Reversal of inhibition by no-modulation training but not by extinction in human causal learning

One of the many strengths of the Rescorla and Wagner (1972) model is that it accounts for both excitatory and inhibitory learning using a single error-correction mechanism. However, it makes the counterintuitive prediction that nonreinforced presentations of an inhibitory stimulus will lead to extinction of its inhibitory properties. Zimmer-Hart and Rescorla (1974) provided the first of several animal conditioning studies that contradicted this prediction. However, the human data are more mixed. Accordingly, we set out to test whether extinction of an inhibitor occurs in human causal learning after simultaneous feature negative training with a conventional unidirectional outcome. In 2 experiments with substantial sample sizes, we found no evidence of extinction after presentations of the inhibitory stimulus alone in either a summation test or causal ratings. By contrast, 2 "no-modulation" procedures that contradicted the original training contingencies successfully reversed inhibition. These results did not differ substantially as a function of participants' self-reported causal structures (configural/modulation/prevention). We hypothesize that inhibitory learning may be intrinsically modulatory, analogous to negative occasion-setting, even with simultaneous training. This hypothesis would explain why inhibition is reversed by manipulations that contradict modulation but not by simple extinction, as well as other properties of inhibitory learning such as imperfect transfer to another excitor. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Individual differences in stimulus identification, rule induction, and generalization of learning

In the field of stimulus generalization, an old yet unresolved discussion pertains to what extent stimulus misidentifications contribute to the pattern of conditioned responding. In this article, we perform cluster analysis on six datasets (four published datasets and two unpublished datasets, included N = 950) to examine the relationship between interindividual differences in (a) stimulus identification, (b) patterns of generalized responding, and (c) verbalized generalization rules. The datasets were obtained from online predictive learning tasks where participants learned associations between colored cues and the presence or absence of a hypothetical outcome. In these datasets, stimulus identification and expectancy ratings were assessed in separate phases to a range of colors varying between blue-green. Using cluster analyses on performance during stimulus identification, we identified different subgroups of participants (good vs. bad identifiers). In all six datasets, we found a close relationship between the pattern of stimulus identification and the shape of the expectancy gradient across the test dimension between the identified subgroups. Furthermore, participants classified as good identifiers were more likely to report a similarity generalization rule than a relational or linear rule, suggesting that individual differences in stimulus identification are related to individual differences in generalization rules. These findings suggest that greater consideration should be given to interindividual variability in stimulus identification, inductive rules, and their relationship in explaining patterns of generalized responses. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Generalization following symmetrical intradimensional discrimination training

A challenge for generalization models is to specify how excitation generated from a CS+ (i.e., positive evidence) should interact with inhibition from a CS- (i.e., negative evidence) to produce generalized responding. Empirically, many generalization phenomena are consistent with the monotonicity principle, which states that additional positive evidence should increase generalized responding, whereas additional negative evidence should decrease responding. However, a recent study (Lee et al.,, 2019) demonstrated that additional negative evidence can sometimes increase generalization, in direct contrast to animal data and associative accounts of generalization. The current study investigated whether a similar effect could be found in a symmetrical intradimensional discrimination procedure with two sources of negative evidence (CS-s) located on each side of a CS+. In three experiments, we compared generalization along a green-blue dimension between one group of participants who learned that an aqua-colored shape (CS+) predicted an outcome (Single Positive group) with another group who also learned that both a slightly greener and a slightly bluer shape led to no outcome (Double Negative group). Experiments 1A and 1B showed no effect of the additional negative evidence in increasing generalization around the CS+. However, changing a stimulus feature at test (shape) resulted in a higher gradient peak in the Double Negative group relative to the Single Positive group in Experiment 2. Although this result violates the monotonicity principle, an extended version of Blough's (1975) model applying cue competition to multiple stimulus dimensions (i.e., shape and color) successfully replicated the group differences. Our results suggest that associative mechanisms can account for some instances in which negative evidence increases generalization. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Inhibitory summation as a form of generalization

Inhibitory learning after feature negative training (A+/AB-) is typically measured by combining the Feature B with a separately trained excitor (e.g., C) in a summation test. Reduced responding to C is taken as evidence that B has properties directly opposite to those of C. However, in human causal learning, transfer of B's inhibitory properties to another excitor is modest and depends on individual differences in inferred causal structure. Here we ask whether instead of opposing processes, a summation test might instead be thought of in terms of generalization. Using an allergist task, we tested whether inhibitory transfer would be influenced by similarity. We found that transfer was greater when the test stimuli were from the same semantic category as the training stimuli (Experiments 1 and 2) and when the test excitor had previously been associated with the same outcome (Experiment 3). We also found that the similarity effect applied across all self-reported causal structures. We conclude it may be more helpful to consider transfer of inhibition as a form of conceptual generalization rather than the arithmetic summation of opposing processes. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Nonreactive testing: Evaluating the effect of withholding feedback in predictive learning

Learning of cue-outcome relationships in associative learning experiments is often assessed by presenting cues without feedback about the outcome and informing participants to expect no outcomes to occur. The rationale is that this "no-feedback" testing procedure prevents new learning during testing that might contaminate the later test trials. We tested this assumption in 4 predictive learning experiments where participants were tasked with learning which foods (cues) were causing allergic reactions (the outcome) in a fictitious patient. We found that withholding feedback in a block of trials had no effect on causal ratings (Experiments 1 and 2), but it led to regression toward intermediate ratings when the missing feedback was embedded in the causal scenario and information about the outcome replaced by a "?" (Experiment 3). A factorial experiment manipulating cover story and feedback revealed that the regression-to-baseline effect was primarily driven by presentation of the "?" feedback (Experiment 4). We conclude that the procedure of testing without feedback, used widely in studies of human cognition, is an appropriate way of assessing learning, as long as the missing data are attributed to the experimenter and the absence of feedback is not highlighted in a way that induces uncertainty. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Second-Order Conditioning in Humans

In contrast to the large body of work demonstrating second-order conditioning (SOC) in non-human animals, the evidence for SOC in humans is scant. In this review, I examine the existing literature and suggest theoretical and procedural explanations for why SOC has been so elusive in humans. In particular, I discuss potential interactions with conditioned inhibition, whether SOC is rational, and propose critical parameters needed to obtain the effect. I conclude that SOC is a real but difficult phenomenon to obtain in humans, and suggest directions for future research.

Punishment insensitivity in humans is due to failures in instrumental contingency learning

Punishment maximises the probability of our individual survival by reducing behaviours that cause us harm, and also sustains trust and fairness in groups essential for social cohesion. However, some individuals are more sensitive to punishment than others and these differences in punishment sensitivity have been linked to a variety of decision-making deficits and psychopathologies. The mechanisms for why individuals differ in punishment sensitivity are poorly understood, although recent studies of conditioned punishment in rodents highlight a key role for punishment contingency detection (Jean-Richard-Dit-Bressel et al., 2019). Here, we applied a novel ‘Planets and Pirates’ conditioned punishment task in humans, allowing us to identify the mechanisms for why individuals differ in their sensitivity to punishment. We show that punishment sensitivity is bimodally distributed in a large sample of normal participants. Sensitive and insensitive individuals equally liked reward and showed similar rates of reward-seeking. They also equally disliked punishment and did not differ in their valuation of cues that signalled punishment. However, sensitive and insensitive individuals differed profoundly in their capacity to detect and learn volitional control over aversive outcomes. Punishment insensitive individuals did not learn the instrumental contingencies, so they could not withhold behaviour that caused punishment and could not generate appropriately selective behaviours to prevent impending punishment. These differences in punishment sensitivity could not be explained by individual differences in behavioural inhibition, impulsivity, or anxiety. This bimodal punishment sensitivity and these deficits in instrumental contingency learning are identical to those dictating punishment sensitivity in non-human animals, suggesting that they are general properties of aversive learning and decision-making.

Inhibitory causal structures in serial and simultaneous feature negative learning

We have previously reported that human participants trained with a simultaneous feature negative discrimination (intermixed A+/AB− trials) show only modest transfer of inhibitory properties of feature B to a separately trained excitor in a summation test. Their self-reported causal structure suggested that many participants learned that the effect of feature B was somewhat specific to the excitor it had been trained with (modulation), rather than learning that the feature prevented the outcome (prevention). This pattern is reminiscent of the distinction between negative occasion-setting and conditioned inhibition in the animal conditioning literature. However, in animals, occasion-setting is more commonly seen with a serial procedure, in which the feature (B) precedes the training excitor (A). Accordingly, we ran three experiments to compare serial with simultaneous training in an allergist causal judgement task. Transfer in a summation test was stronger to a previously modulated test excitor compared to a simple excitor after both simultaneous and serial training. There was a numerical trend towards a larger effect in the serial group, but it failed to reach significance and the Bayes Factor indicated support for the null. Serial training had no differential effect on the self-reported causal structure and did not significantly reduce overall transfer. After both simultaneous and serial training, transfer was strongest in participants who reported a prevention structure, replicating and extending our previous results to a previously modulated excitor. These results suggest that serial feature negative training does not promote a qualitatively different inhibitory causal structure compared to simultaneous training in humans.

Differences in perceptual memory determine generalization patterns

Although memory of past experiences is crucial for the ability to transfer knowledge to new situations, surprisingly little research has directly investigated the relationship between memory and generalization. The present study sought to investigate how the perceptual memory of a trained stimulus influences generalization to similar stimuli. Forty participants underwent a fear conditioning procedure on Day 1, and separate memory recall and generalization tests on Day 2. We focused on two aspects of perceptual memory: namely memory bias (i.e., over- or underestimation of stimulus magnitude) and uncertainty. We found that memory bias predicted the pattern of generalized self-reported (expectancy ratings) and psychophysiological responses (fear-potentiated startle responses). Memory uncertainty was measured in two ways: self-reported uncertainty ratings and variability in stimulus recall. We found that higher levels of self-reported memory uncertainty corresponded with a broader generalization gradient on US expectancy, while greater variability in memory recall was associated with a broader generalization gradient on fear-potentiated startle responses. Taken together, our findings suggest that memory is an important determinant of generalized behavior and illustrate the need to account for these interindividual differences in perceptual memory when examining the generalization of learned responses.

Acute Bilateral Uveitis, Hypotony, and Cataracts Associated with Ipilimumab and Nivolumab Therapy: Optical Coherence Tomography Angiography Findings

Immune checkpoint inhibitors are increasingly being used for the treatment of several malignancies. In rare cases, patients develop disabling ophthalmic side effects such as dry eyes, episcleritis, keratitis, uveitis, inflammatory orbitopathy, myasthenia gravis, macular edema, and serous retinal detachment. We present a case of acute bilateral anterior uveitis, prolonged hypotony, and cataracts following the use of dual therapy ipilimumab and nivolumab. Physicians should be aware of these immune-mediated ocular adverse events and should have a management plan to deal with these side effects that range from mild to vision threatening.

Individual differences in causal structures inferred during feature negative learning

Traditional associative learning theories predict that training with feature negative (A+/AB-) contingencies leads to the feature B acquiring negative associative strength and becoming a conditioned inhibitor (i.e., prevention learning). However, feature negative training can sometimes result in negative occasion setting, where B modulates the effect of A. Other studies suggest that participants learn about configurations of cues rather than their individual elements. In this study, we administered simultaneous feature negative training to participants in an allergist causal learning task and tested whether evidence for these three types of learning (prevention, modulation, configural) could be captured via self-report in the absence of any procedural manipulation. Across two experiments, we show that only a small subset of participants endorse the prevention option, suggesting that traditional associative models that predict conditioned inhibition do not completely capture how humans learn about negative contingencies. We also show that the degree of transfer in a summation test corresponds to the implied causal structure underlying conditioned inhibition, occasion-setting, and configural learning, and that participants are only partially sensitive to explicit hints about causal structure. We conclude that feature negative training is an ambiguous causal scenario that reveals individual differences in the representation of inhibitory associations, potentially explaining the modest group-level inhibitory effects often found in humans.

Modelling generalisation gradients as augmented Gaussian functions

Studying generalisation of associative learning requires analysis of response gradients measured over a continuous stimulus dimension. In human studies, there is often a high degree of individual variation in the gradients, making it difficult to draw conclusions about group-level trends with traditional statistical methods. Here, we demonstrate a novel method of analysing generalisation gradients based on hierarchical Bayesian curve-fitting. This method involves fitting an augmented (asymmetrical) Gaussian function to individual gradients and estimating its parameters in a hierarchical Bayesian framework. We show how the posteriors can be used to characterise group differences in generalisation and how classic generalisation phenomena such as peak shift and area shift can be measured and inferred. Estimation of descriptive parameters can provide a detailed and informative way of analysing human generalisation gradients.

Polymicrobial infection confined to Ahmed glaucoma shunt

Purpose

To present a case of a unique complication of an Ahmed glaucoma shunt. The pathological and immunohistochemical findings will also be discussed.

Observations

A 58-year-old woman with glaucoma secondary to Marfan syndrome and cataract surgery developed exposure of an Ahmed glaucoma tube, intraluminal white inflammatory material, and low-grade endophthalmitis five years after insertion. The patient was treated with topical and oral antibiotics and successfully underwent removal and replacement of the shunt. Pathologic analysis of the intraluminal contents revealed a bacterial infiltrate of mixed morphology.

Conclusions and Importance

Concurrent tube exposure, intraluminal exudates, and endophthalmitis is a rare but potentially serious complication of glaucoma drainage device surgery. When this complication is encountered, prompt medical and surgical intervention is necessary to prevent significant vision loss. Ultimately, the glaucoma shunt may be revised, replaced, or removed altogether from the eye.

Comparison of 1-field, 2-fields, and 3-fields fundus photography for detection and grading of diabetic retinopathy

AIM

To evaluate the sensitivity and specificity of 1-, 2-, and 3-fields, nonmydriatic (NM), 45° color photography compared with mydriatic ophthalmoscopy for detection of diabetic retinopathy (DR).

METHODS

Masked, comparative case series was performed utilizing a group of 128 diabetic patients (256 eyes) with various stages of DR who underwent both 3-fields NM color photography and ophthalmologic examination. In a blinded manner, the same optometrist who read the original 3-fields images for a patient read the 1- and 2-fields photographs on separate dates later.

RESULTS

The sensitivity and specificity of digital retinal photography compared with dilated ophthalmoscopy were, respectively: 88% and 76% for 1-field; 94% and 69% for 2-fields; and 100% and 79% for 3-fields. The proportion of agreement between fundus photography reading and exam DR diagnosis were 58% for 1-field, 58% for 2-fields, and 77% for 3-fields. Kappa and Cramer's V statistics for 1-, 2-, and 3-fields were 0.55 and 0.60, 0.52 and 0.57, and 0.72 and 0.74, respectively. Three-fields measurement of DR was most similar to the dilated ophthalmological exam overall and across all DR severity levels.

CONCLUSIONS

Compared to 1- and 2-fields fundus photography, 3-fields is superior for detecting vision-threatening DR. One- and 2-fields have reasonable sensitivity for DR screening.