Weak correlations between visual abilities in healthy older adults, despite long-term performance stability.

Using batteries of visual tests, most studies have found that there are only weak correlations between the performance levels of the tests. Factor analysis has confirmed these results. This means that a participant excelling in one test may rank low in another test. Hence, there is very little evidence for a common factor in vision. In visual aging research, cross-sectional studies have repeatedly found that healthy older adults' performance is strongly deteriorated in most visual tests compared to young adults. However, also within the healthy older population, there is no evidence for a visual common factor. To investigate whether the weak between-tests correlations are due to fluctuations in individual performance throughout time, we conducted a longitudinal study. Healthy older adults performed a battery of eight visual tests, with two re-tests after approximately four and seven years. Pearson's, Spearman's and intraclass correlations of most visual tests were significant across the three testing, indicating that the tests are reliable and individual differences are stable across years. Yet, we found low between-tests correlations at each visit, which is consistent with previous studies finding no evidence for a visual common factor. Our results exclude the possibility that the weak correlations between tests are due to high within-individual variance across time.

No Common Factor Underlying Decline of Visual Abilities in Mild Cognitive Impairment.

INTRODUCTION: Recent work has shown an association between cognitive and visual impairments and two main theories were advanced, namely the sensory deprivation and the common cause theories. Most studies considered only basic visual functions such as visual acuity or visual field size and evaluated the association with dementia. OBJECTIVES: To reconcile between these theories and to test the link between visual and cognitive decline in mildly cognitive impaired people. METHODS: We employed a battery of 19 visual tasks on 39 older adults with mild cognitive impairment and 91 without any evidence of cognitive decline, as measured by the Montreal Cognitive Assessment. RESULTS: Our results show a strong association between visual impairment and mild cognitive impairment. In agreement with previous results with younger and healthy older adults, we found also only weak correlations between most tests in older adults with mild cognitive impairment. CONCLUSION: Our results suggest that visual and cognitive abilities decline simultaneously, but they do so independently across visual and cognitive functions and across participants.

Portable bioluminescent platform for in vivo monitoring of biological processes in non-transgenic animals.

Bioluminescent imaging (BLI) is one of the most powerful and widely used preclinical imaging modalities. However, the current technology relies on the use of transgenic luciferase-expressing cells and animals and therefore can only be applied to a limited number of existing animal models of human disease. Here, we report the development of a "portable bioluminescent" (PBL) technology that overcomes most of the major limitations of traditional BLI. We demonstrate that the PBL method is capable of noninvasive measuring the activity of both extracellular (e.g., dipeptidyl peptidase 4) and intracellular (e.g., cytochrome P450) enzymes in vivo in non-luciferase-expressing mice. Moreover, we successfully utilize PBL technology in dogs and human cadaver, paving the way for the translation of functional BLI to the noninvasive quantification of biological processes in large animals. The PBL methodology can be easily adapted for the noninvasive monitoring of a plethora of diseases across multiple species.

Individual differences in the perception of visual illusions are stable across eyes, time, and measurement methods.

Vision scientists have tried to classify illusions for more than a century. For example, some studies suggested that there is a unique common factor for all visual illusions. Other studies proposed that there are several subclasses of illusions, such as illusions of linear extent or distortions. We previously observed strong within-illusion correlations but only weak between-illusion correlations, arguing in favor of an even higher multifactorial space with-more or less-each illusion making up its own factor. These mixed results are surprising. Here, we examined to what extent individual differences in the perception of visual illusions are stable across eyes, time, and measurement methods. First, we did not find any significant differences in the magnitudes of the seven illusions tested with monocular or binocular viewing conditions. In addition, illusion magnitudes were not significantly predicted by visual acuity. Second, we observed stable individual differences over time. Last, we compared two illusion measurements, namely an adjustment procedure and a method of constant stimuli, which both led to similar individual differences. Hence, it is unlikely that the individual differences in the perception of visual illusions arise from instability across eyes, time, and measurement methods.

How does positive mood modulate time-based event expectancy?

In the present study, we investigated how positive mood affects the formation of time-based event expectancies. After positive or neutral mood inductions, participants performed a binary choice response task in which two target stimuli (circle and square) and two pre-target intervals (800 and 1600 ms) appeared equally often. One of the targets was paired with the short interval and the other target with the long interval in 90% of the trials. We found that participants from the positive and neutral groups showed markedly different behavioral patterns of time-based expectancy. The time-based expectancy was restricted to shorter intervals for the positive group and to longer intervals for the neutral group. We propose that positive mood increases attentional prioritization of information that is temporally closer to us.

How stable is perception in #TheDress and #TheShoe?

#TheDress is perceived by some people as black and blue while others perceive it as white and gold. We have previously shown that the first encounter with #TheDress strongly biases its perception. This percept remained stable during the experiment, suggesting a role of one-shot learning. #TheShoe is another image that elicits similar bimodal color percepts. Here, we investigated how percepts change over time in both #TheShoe and #TheDress. First, we show that the important role of one-shot learning, which we found for #TheDress extends to #TheShoe. Similarly to our previous results with the dress, hiding large parts of the image with occluders biased the percept of the shoe. The percept did not change for the majority of observers when the occluders were removed. Second, we investigated if and how percepts switch over a time course of 14 days. We found that although some observers experienced percept switches, the percept was largely stable for most observers.

Associations between genetic variations and global motion perception.

The cholinergic system is known to strongly modulate perceptual and cognitive processes, and the alpha7 subunit of the cholinergic nicotinic receptor (CHRNA7) is broadly expressed within the visual system. Here, we assessed whether genetic variations of CHRNA7 affect coherent motion perception. Motion perception has been shown to decline with age, and it has previously been suggested that the effects of genetic variations are magnified by age. Therefore, we tested both older (n = 62) and younger adults (n = 63). We found that motion coherence thresholds were significantly higher for older compared to younger adults, which is in accordance with previous studies. Interestingly, there was a strong relationship between variants of the SNP rs2337980 of the CHRNA7 and motion direction discrimination. In particular, participants carrying the TC genotype had considerably lower motion coherence thresholds than CC carriers. The effect of genotype did not interact with age. Our results show that genetic variations are associated with perceptual performance, but are unlikely to explain age-related changes.

No evidence for a common factor underlying visual abilities in healthy older people.

The world's population is aging at an increasing rate. Even in the absence of neurodegenerative disorders, healthy aging affects perception and cognition. In the context of cognition, common factors are well established. Much less is known about common factors for vision. Here, we tested 92 healthy older and 104 healthy younger participants in 19 visual tests (including visual search and contrast sensitivity) and three cognitive tests (including verbal fluency and digit span). Unsurprisingly, younger participants performed better than older participants in almost all tests. Surprisingly, however, the performance of older participants was mostly uncorrelated between visual tests, and we found no evidence for a common factor. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Children with autism spectrum disorder show increased sensitivity to time-based predictability.

Objectives: We studied timed-based expectancy as well as general perceptual-motor speed in children with autism spectrum disorder (ASD). Methods: In Experiment 1, 11 children with ASD and 11 typically developing children (TD) (6-13 years) completed a binary choice response task in which foreperiod duration predicted the response target's location with a probability of 0.8. In Experiment 2, we compared performance between 10 children with ASD (6-11 years) and 10 TD children by using a simple reaction time test. Results: Employing a binary forced choice task where the duration of a pre-target interval (800 or 1400 ms) probabilistically predicted the target, we found that children with ASD were sensitive to the temporal regularity, whereas TD children were not. Children with ASD were faster for expected combinations of interval and target location but they were also less accurate for those combinations. Results from an additional simple reaction time test indicate that the development of general perceptual-motor processes was delayed in children with ASD. However, the ability for children with ASD to form time-based expectancies was not correlated with their performance in the simple reaction time test. Conclusion: Children with ASD show significantly greater sensitivity towards time-based predictability than TD children. However, the development of general perceptual-motor processes was impaired in children with ASD.

Sex-related differences in vision are heterogeneous.

Despite well-established sex differences for cognition, audition, and somatosensation, few studies have investigated whether there are also sex differences in visual perception. We report the results of fifteen perceptual measures (such as visual acuity, visual backward masking, contrast detection threshold or motion detection) for a cohort of over 800 participants. On six of the fifteen tests, males significantly outperformed females. On no test did females significantly outperform males. Given this heterogeneity of the sex effects, it is unlikely that the sex differences are due to any single mechanism. A practical consequence of the results is that it is important to control for sex in vision research, and that findings of sex differences for cognitive measures using visually based tasks should confirm that their results cannot be explained by baseline sex differences in visual perception.

Time-based event expectancies in children with Autism spectrum disorder.

Here, we studied the time-based event expectancies in children with Autism spectrum disorder. Nine children with Autism spectrum disorders and ten (6-11 years) typically developing children participated. In a choice-response task with two different pre-target intervals, participants had to indicate the left or right direction of a target stimulus. The target was predicted by the duration of the pre-target interval with 80% validity. We found that, in children with Autism spectrum disorder, in contrast to typically developing children, the formation of time-based event expectancies was restricted to the relatively longer pre-target interval. This pattern is rather typical for healthy young adults. These findings indicate that children with Autism spectrum disorder are able to form time-based event expectancies, and that, similar to healthy young adults, longer pre-target intervals enable them to make more optimal temporal predictions.

The role of one-shot learning in #TheDress.

#TheDress is remarkable in two aspects. First, there is a bimodal split of the population in the perception of the dress's colors (white/gold vs. black/blue). Second, whereas interobserver variance is high, intra-observer variance is low, i.e., the percept rarely switches in a given individual. There are two plausible routes of explanations: either one-shot learning during the first presentation of the image splits observers into two different, stable populations, or the differences are caused by stable traits of observers, such as different visual systems. Here, we hid large parts of the image by white occluders. The majority of naïve participants perceived the dress as black and blue. With black occluders, the majority of observers perceived the dress as white and gold. The percept did not change when we subsequently presented the full image, arguing for a crucial role of one-shot learning. Next, we investigated whether the first fixation determines the perceived color in naïve observers. We found no such effect. It remains thus a puzzling question where the source of variability in the different percepts comes from.

Spatial and temporal aspects of visual backward masking in children and young adolescents.

The development of visual functions is very diverse. Some visual functions mature within the first year of life, whereas maturation for other functions extends into adolescence. The reasons for these developmental differences are largely unknown. Here, we investigated spatiotemporal processing in children (7-9 years, n = 15), young adolescents (11-13 years, n = 26), and adults (18-33 years, n = 24) using the shine-through visual backward-masking paradigm. We found that children had significantly longer vernier durations than either young adolescents or adults. However, children's spatial and temporal processing of complex masks was very similar to that of young adolescents and adults. We suggest that spatiotemporal processing related to visual backward masking is already fully developed at age 7, whereas the attentional processes related to target enhancement only mature in young adolescence.

Effects of alcohol intake on time-based event expectations.

Previous evidence suggests that alcohol affects various forms of temporal cognition. However, there are presently no studies investigating whether and how alcohol affects on time-based event expectations. Here, we investigated the effects of alcohol on time-based event expectations. Seventeen healthy volunteers, aged between 19 and 36 years, participated. We employed a variable foreperiod paradigm with temporally predictable events, mimicking a computer game. Error rate and reaction time were analyzed in placebo (0 g/kg), low dose (0.2 g/kg) and high dose (0.6 g/kg) conditions. We found that alcohol intake did not eliminate, but substantially reduced, the formation of time-based expectancy. This effect was stronger for high doses, than for low doses, of alcohol. As a result of our studies, we have evidence that alcohol intake impairs time-based event expectations. The mechanism by which the level of alcohol impairs time-based event expectations needs to be clarified by future research.

Ageing and visual spatiotemporal processing.

Ageing affects many visual functions. Here, we investigated the effects of ageing on vernier acuity and backward masking using the shine-through paradigm. We divided healthy older adults (>60 years) into two groups depending on whether vernier duration was comparable to younger adults (Older Adults 1) or not (Older Adults 2). Backward masking was deteriorated for Older Adults 2 but not for Older Adults 1. In addition, by using complex masking gratings, we found deficits in spatial and temporal vision in Older Adults 2, which cannot be explained by deteriorated visual acuity, pointing to cortical rather than retinal causes. Our results highlight the importance of taking into account individual differences in visual ageing research. In addition, our results have important implications for schizophrenia. Schizophrenia has been suggested to be a form of early brain ageing. Linking our current masking results in ageing to previous masking results in schizophrenia shows that schizophrenia is not a form of early ageing, at least not in the visual domain.

Time-based event expectations employ relative, not absolute, representations of time.

When the timing of an event is predictable, humans automatically form implicit time-based event expectations. We investigated whether these expectations rely on absolute (e.g., 800 ms) or relative (e.g., a shorter duration) representations of time. In a choice-response task with two different pre-target intervals, participants implicitly learned that targets were predictable by interval durations. In a test phase, the two intervals were either considerably shortened or lengthened. In both cases, behavioral tendencies transferred from practice to test according to relative, not absolute, interval duration. We conclude that humans employ relative representations of time periods when forming time-based event expectations. These results suggest that learned time-based event expectations (e.g., in communication and human-machine interaction) should transfer to faster or slower environments if the relative temporal distribution of events is preserved.

Small effects of smoking on visual spatiotemporal processing.

Nicotine is an important stimulant that is involved in modulating many neuronal processes, including those related to vision. Nicotine is also thought to play a key role in schizophrenia: A genetic variation of the cholinergic nicotine receptor gene, alpha-7 subunit (CHRNA7) has been shown to be associated with stronger backward masking deficits in schizophrenic patients. In this study, we tested visual backward masking in healthy smokers and non-smokers to further understand the effects of nicotine on spatiotemporal vision. In the first study, we tested 48 participants, a group of non-smokers (n = 12) and three groups of regular smokers that were either nicotine deprived (n = 12), non-deprived (n = 12) or deprived but were allowed to smoke a cigarette directly before the start of the experiment (n = 12). Performance was similar across groups, except for some small negative effects in nicotine-deprived participants. In the second study, we compared backward masking performance between regular smokers and non-smokers for older (n = 37, 13 smokers) and younger (n = 67, 21 smokers) adults. Older adults performed generally worse than younger adults but there were no significant differences in performance between smokers and non-smokers. Taken together, these findings indicate that nicotine has no long-term negative effects on visual spatiotemporal processing as determined by visual backward masking.

How alcohol intake affects visual temporal processing.

Alcohol affects vision. However, the influence of alcohol on visual processing is largely unknown. Here, we investigated the effects of alcohol on visual spatiotemporal processing. We employed a visual paradigm, the shine through backward masking paradigm, in which a vernier is either presented alone or followed by a variety of mask. We investigated performance for women at blood alcohol levels of 0mg/kg, 400mg/kg and 600 mg/kg and for men at 0mg/kg, 400mg/kg and 800 mg/kg. When the vernier was presented alone, vernier offset discrimination was not affected by alcohol. When the vernier was followed by a mask, stimulus onset asynchronies (SOAs) between target and mask were significantly longer after alcohol intake. However, as a second experiment showed, spatial and temporal processing per se were not impaired by alcohol. In addition, spatial processing was not affected by moderate alcohol consumption. Hence, moderate consumption of alcohol does not affect visual processing per se. We propose that the longer SOAs after alcohol intake are related to changes in mechanisms of target stabilization rather than changes in spatial and temporal sensitivity as has been previously suggested.

Age-related changes in visually evoked electrical brain activity.

Whereas much is known about the degenerative effects of aging on cortical tissue, less is known about how aging affects visually evoked electrical activity, and at what latencies. We compared visual processing in elderly and young controls using a visual masking paradigm, which is particularly sensitive to detect temporal processing deficits, while recording EEG. The results show that, on average, elderly have weaker visual evoked potentials than controls, and that elderly show a distinct scalp potential topography (microstate) at around 150 ms after stimulus onset. This microstate occurred irrespective of the visual stimulus presented. Electrical source imaging showed that the changes in the scalp potential resulted from decreased activity in lateral occipital cortex and increases in fronto-parietal areas. We saw, however, no evidence that increased fronto-parietal activity enhanced performance on the discrimination task, and no evidence that it compensated for decreased posterior activity. Our results show qualitatively different patterns of visual evoked potentials (VEPs) in the elderly, and demonstrate that increased fronto-parietal activity arises during visual processing in the elderly already between 150 and 200 ms after stimulus onset. The microstate associated with these changes is a potential diagnostic tool to detect age-related cortical changes.