Color constancy for daylight illumination changes in anomalous trichromats and dichromats.

Color constancy is the perceptual stability of surface colors under temporal changes in the illumination spectrum. The illumination discrimination task (IDT) reveals worse discrimination for "bluer" illumination changes in normal-trichromatic observers (changes towards cooler color temperatures on the daylight chromaticity locus), indicating greater stability of scene colors or better color constancy, compared with illumination changes in other chromatic directions. Here, we compare the performance of individuals with X-linked color-vision deficiencies (CVDs) to normal trichromats on the IDT performed in an immersive setting with a real scene illuminated by spectrally tunable LED lamps. We determine discrimination thresholds for illumination changes relative to a reference illumination (D65) in four chromatic directions, roughly parallel and orthogonal to the daylight locus. We find, using both a standard CIELUV metric and a cone-contrast metric tailored to distinct CVD types, that discrimination thresholds for daylight changes do not differ between normal trichromats and CVD types, including dichromats and anomalous trichromats, but thresholds for atypical illuminations do differ. This result extends a previous report of illumination discrimination ability in dichromats for simulated daylight changes in images. In addition, using the cone-contrast metric to compare thresholds for bluer and yellower daylight changes with those for unnatural redder and greener changes, we suggest that reduced sensitivity to daylight changes is weakly preserved in X-linked CVDs.

Do EnChroma glasses improve performance on clinical tests for red-green color deficiencies?

We investigated the claims of EnChroma that their notch filters aid chromatic discrimination in color-vision deficiencies (CVD). Few research studies have addressed these claims and reports are still inconclusive, mainly due to small sample sizes. We here add to previous research finding little evidence to support the benefits of EnChroma lenses. Comparing the performance of 86 well-categorized CVD observers and 24 controls on two clinical tests we report no overall improvement when EnChroma lenses were worn. In line with previous studies, our results imply an improvement in discrimination for some colors while worsening discrimination for others. A model was constructed computing discrimination changes for different groups of ideal observers corroborating our behavioral outcomes. Taken together, our results do not support the use of EnChroma notch filters for the improvement of color discrimination in CVD.

Automatic processing of emotional stimuli in euthymic patients with bipolar disorder.

BACKGROUND: Biased information processing styles are a core feature of cognitive models of unipolar depression (UD). The manic-defence hypothesis (MDH) posits that UD and Bipolar Disorder (BD) are subject partially to the same underlying cognitive processes, which may act as putative vulnerability factors. Previous studies have used experimental paradigms as a way of measuring automatic (non-intentional) processing of emotional information in order to test the MDH with some studies providing some evidence for a negatively biased automatic processing of emotionally-relevant information in BD. However, most prior studies used supraliminal stimuli (i.e. presented above perceptual threshold). Based on the MDH we predicted that subliminally presented negative stimuli will affect performance of patients with BD differently than non-clinical participants, but similarly to what has been observed in prior studies with currently depressed patients. METHODS: The current study used an affective priming paradigm with both supraliminally and subliminally presented emotional images as primes to measure automatic processing. Seventeen euthymic individuals with a BD diagnosis were recruited along with seventeen non-clinical control participants (NCC) matched for age and gender. RESULTS: We found interference (increased response times) due to masked, subliminally presented negative primes in patients with BD when negative prime images were followed by negative targets, but decreased response times (facilitation) in NCCs. LIMITATIONS: We did not include a psychiatric control group and the sample size was small. CONCLUSION: Our findings suggest that euthymic patients with BD do exhibit an affective bias suggesting an increased sensitivity to negative emotional information even when euthymic.

The role of negative mood induction on working memory capacity in individuals putatively at risk for bipolar disorder: A pilot study.

OBJECTIVE: Bipolar disorder (BD) is characterized by cognitive deficits. Usually individuals at risk for BD do not exhibit such deficits but they might be evident under cognitive or emotionally stressful conditions. To our knowledge this is the first study examining working memory capacity under mood induction in individuals at risk for BD. METHODS: Using the Hypomanic Personality Scale (HPS) 68 participants out of an initial pool of 148 students were divided into groups at high and low risk for BD. They completed twice a Dual Task Paradigm (DTP) task assessed under high and low cognitive load prior to and following a negative mood induction. RESULTS: As expected stimuli incongruency, high cognitive load and mood induction increased response times. Contrary to our hypothesis the mood induction did not differentially affect at-risk individuals. However, they generally reacted faster to neutral stimuli compared to those at low risk. CONCLUSIONS: While we replicated former results related to the DTP, we did not find evidence for the hypothesis that individuals putatively at risk for BD will be more affected by negative mood when doing such a cognitive task. Replication using a larger sample is needed which should also examine whether changes in positive mood might more relevant in the context of risk for mania.

Vulnerability for mania - is it linked to problems delaying gratification?

Impulsivity is described as one of the main risk factors for mania. One facet of impulsivity, the inability to delay gratification, might be of special relevance, because a hypersensitivity to reward is hypothesized to be related to mania. The main aim of this study was to examine whether risk for mania is associated with deficits in the ability to delay gratification using both a behavioral and a self-report (UPPS) measure. An additional reason for choosing the UPPS was to see if prior results about an association between risk for mania and positive urgency could be replicated. Thirty-three individuals at risk for mania and a matched control group were selected using the Hypomanic Personality Scale and interviewed for a history of mood disorders. The main outcome measures were the Single-Key-Impulsivity-Paradigm and Monetary Choice Questionnaire. The groups did not differ in measures of gratification delay but we replicated other studies reporting significantly higher levels of positive urgency and sensation seeking in at-risk individuals. We suggest that individuals at risk might not generally be more impulsive but rather that impulsive behaviors might be triggered in response to specific mood states.

Counterphase modulation photometry: comparison of two instruments.

The ratio of long-wavelength to medium-wavelength sensitive cones varies significantly among people. In order to investigate the possible effect of this variation in large numbers of participants, a quick and efficient method to estimate the ratio is required. The OSCAR test has been utilized previously for this purpose, but it is no longer available commercially. Having access to one of the few remaining OSCAR instruments, we compared the observers' mean settings to those obtained with the Medmont C100, a newer but apparently similar device. We also obtained Rayleigh matches for each participant. One hundred volunteers took part in the study. Settings on the OSCAR test were highly correlated with those on the Medmont C100. Both tests appeared to be influenced not only by L∶M cone ratios but also by the spectral positions of the cone photopigments, since anomaloscope midmatch points accounted for a significant proportion of the variance. We conclude that the Medmont C100 can be used as a suitable replacement for the OSCAR test and has a role in the rapid estimation of L∶M cone ratios.

Is risk for mania associated with increased daydreaming as a form of mental imagery?

BACKGROUND: Bipolar disorder and risk for mania are associated with setting high goals and dysregulated goal pursuit. One mechanism mediating between setting high goals and manic symptoms could be daydreaming or more generally, mental imagery. 'Daydreams' (as one form of mental imagery) are characterized by the fact that the content is produced deliberately. Akiskal et al. (1995) reported that daydreaming prospectively predicted a switch from unipolar depression to bipolar disorder. We here hypothesized that risk for mania should also be associated with increased daydreaming after controlling for depression. METHOD: N=249 participants from a non-clinical, community sample completed several self-report measures including the Hypomanic Personality scale and Daydreaming scale. RESULTS: Hierarchical regression revealed that risk for mania predicted daydreaming after controlling for current and former depression. LIMITATIONS: Only self-report measures were used. The sample was a non-clinical, primarily White British sample, which has implications for generalizability. CONCLUSIONS: Despite limitations our results support the hypothesis that vulnerability for mania is associated with daydreaming. Daydreaming was related to mania and depression which highlights that it might be relevant for the etiology or maintenance of mood disorders.

The dimensionality of color vision in carriers of anomalous trichromacy.

Some 12% of women are carriers of the mild, X-linked forms of color vision deficiencies called "anomalous trichromacy." Owing to random X chromosome inactivation, their retinae must contain four classes of cone rather than the normal three; and it has previously been speculated that these female carriers might be tetrachromatic, capable of discriminating spectral stimuli that are indistinguishable to the normal trichromat. However, the existing evidence is sparse and inconclusive. Here, we address the question using (a) a forced-choice version of the Rayleigh test, (b) a test using multidimensional scaling to reveal directly the dimensionality of the participants' color space, and (c) molecular genetic analyses to estimate the X-linked cone peak sensitivities of a selected sample of strong candidates for tetrachromacy. Our results suggest that most carriers of color anomaly do not exhibit four-dimensional color vision, and so we believe that anomalous trichromacy is unlikely to be maintained by an advantage to the carriers in discriminating colors. However, 1 of 24 obligate carriers of deuteranomaly exhibited tetrachromatic behavior on all our tests; this participant has three well-separated cone photopigments in the long-wave spectral region in addition to her short-wave cone. We assess the likelihood that behavioral tetrachromacy exists in the human population.