Karin S. Pilz

Effects of aging on biological motion discrimination

Previous studies have shown that older subjects have difficulties discriminating the walking direction of point-light walkers. In two experiments, we investigated the underlying cause in further detail. In Experiment 1, subjects had to discriminate the walking direction of upright and inverted point-light walkers in a cloud of randomly moving dots. In general, older subjects performed less accurately and showed an increased inversion effect. Nevertheless, they were as accurate as young subjects for upright walkers during training, in which no noise was added to the display. These results indicate that older subjects are less able to extract relevant information from noisy displays. In Experiment 2, subjects discriminated the walking direction of scrambled walkers that primarily contained local motion information, random-position walkers that primarily contained global form information, and normal point-light walkers that contained both kinds of information. Both age groups performed at chance when no global form information was present in the display but were equally accurate for walkers that only contained global form information. However, when both local motion and global form information were present in the display, older subjects were less accurate then younger subjects. Older subjects again exhibited an increased inversion effect. These results indicate that both older and younger subjects rely more on global form than local motion to discriminate the direction of point-light walkers. Also, older subjects seem to have difficulties integrating global form and local motion information as efficiently as younger subjects.

Spatiotemporal properties of apparent motion perception and aging

We used a random-dot two-frame apparent motion paradigm to investigate whether age-related declines in motion perception are caused by deficits in integrating spatial information, temporal information, or both. Two random-dot patterns were presented sequentially on a black screen, separated by a blank inter-stimulus interval ranging from 0.01 s to 0.240 s. From the first to the second pattern, all the dots were shifted to the left or right by an equal displacement ranging from 0.03 deg to 1.64 deg. The spatiotemporal range yielding good direction discrimination performance was greatly reduced with age. For ISIs longer than 0.04 s, older subjects performed less accurately than younger subjects across a wide range of spatial displacements. Older subjects also showed poorer performance for large spatial displacements across a wide range of ISIs. Age-related differences in performance were also found with small displacements; however, these were largely accounted for by age-related declines in visual acuity. Overall, the results show that the maximum temporal interval and maximum spatial displacement over which two frames can be integrated are reduced in older age.

Effects of aging on identifying emotions conveyed by point-light walkers

The visual system is able to recognize human motion simply from point lights attached to the major joints of an actor. Moreover, it has been shown that younger adults are able to recognize emotions from such dynamic point-light displays. Previous research has suggested that the ability to perceive emotional stimuli changes with age. For example, it has been shown that older adults are impaired in recognizing emotional expressions from static faces. In addition, it has been shown that older adults have difficulties perceiving visual motion, which might be helpful to recognize emotions from point-light displays. In the current study, 4 experiments were completed in which older and younger adults were asked to identify 3 emotions (happy, sad, and angry) displayed by 4 types of point-light walkers: upright and inverted normal walkers, which contained both local motion and global form information; upright scrambled walkers, which contained only local motion information; and upright random-position walkers, which contained only global form information. Overall, emotion discrimination accuracy was lower in older participants compared with younger participants, specifically when identifying sad and angry point-light walkers. In addition, observers in both age groups were able to recognize emotions from all types of point-light walkers, suggesting that both older and younger adults are able to recognize emotions from point-light walkers on the basis of local motion or global form.

How Prevalent Is Object-Based Attention?

Previous research suggests that visual attention can be allocated to locations in space (space-based attention) and to objects (object-based attention). The cueing effects associated with space-based attention tend to be large and are found consistently across experiments. Object-based attention effects, however, are small and found less consistently across experiments. In three experiments we address the possibility that variability in object-based attention effects across studies reflects low incidence of such effects at the level of individual subjects. Experiment 1 measured space-based and object-based cueing effects for horizontal and vertical rectangles in 60 subjects comparing commonly used target detection and discrimination tasks. In Experiment 2 we ran another 120 subjects in a target discrimination task in which rectangle orientation varied between subjects. Using parametric statistical methods, we found object-based effects only for horizontal rectangles. Bootstrapping methods were used to measure effects in individual subjects. Significant space-based cueing effects were found in nearly all subjects in both experiments, across tasks and rectangle orientations. However, only a small number of subjects exhibited significant object-based cueing effects. Experiment 3 measured only object-based attention effects using another common paradigm and again, using bootstrapping, we found only a small number of subjects that exhibited significant object-based cueing effects. Our results show that object-based effects are more prevalent for horizontal rectangles, which is in accordance with the theory that attention may be allocated more easily along the horizontal meridian. The fact that so few individuals exhibit a significant object-based cueing effect presumably is why previous studies of this effect might have yielded inconsistent results. The results from the current study highlight the importance of considering individual subject data in addition to commonly used statistical methods.

Age-related changes in matching novel objects across viewpoints

Object recognition is an important visual process. We are not only required to recognize objects across a variety of lighting conditions and variations in size, but also across changes in viewpoint. It has been shown that reaction times in object matching increase as a function of increasing angular disparity between two views of the same object, and it is thought that this is related to the time it takes to mentally rotate an object. Recent studies have shown that object rotations for familiar objects affect older subjects differently than younger subjects. To investigate the general normalization effects for recognizing objects across different viewpoints regardless of visual experience with an object, in the current study we used novel 3D stimuli. Older and younger subjects matched objects across a variety of viewpoints along both in-depth and picture-plane rotations. Response times (RTs) for in-depth rotations were generally slower than for picture plane rotations and older subjects, overall, responded slower than younger subjects. However, a male RT advantage was only found for objects that differed by large, in-depth rotations. Compared to younger subjects, older subjects were not only slower but also less accurate at matching objects across both rotation axes. The age effect was primarily due to older male subjects performing worse than younger male subjects, whereas there was no significant age difference for female subjects. In addition, older males performed even worse than older females, which argues against a general male advantage in mental rotations tasks.

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.

Global form and motion processing in healthy ageing

The ability to perceive biological motion has been shown to deteriorate with age, and it is assumed that older adults rely more on the global form than local motion information when processing point-light walkers. Further, it has been suggested that biological motion processing in ageing is related to a form-based global processing bias. Here, we investigated the relationship between older adults preference for form information when processing point-light actions and an age-related form-based global processing bias. In a first task, we asked older (>60years) and younger adults (19-23years) to sequentially match three different point-light actions; normal actions that contained local motion and global form information, scrambled actions that contained primarily local motion information, and random-position actions that contained primarily global form information. Both age groups overall performed above chance in all three conditions, and were more accurate for actions that contained global form information. For random-position actions, older adults were less accurate than younger adults but there was no age-difference for normal or scrambled actions. These results indicate that both age groups rely more on global form than local motion to match point-light actions, but can use local motion on its own to match point-light actions. In a second task, we investigated form-based global processing biases using the Navon task. In general, participants were better at discriminating the local letters but faster at discriminating global letters. Correlations showed that there was no significant linear relationship between performance in the Navon task and biological motion processing, which suggests that processing biases in form- and motion-based tasks are unrelated.

The effects of aging on perception and cognition

The developed world is aging faster than ever before. Even in the absence of neurodegenerative disease, aging affects all kinds of human functions including perception and cognition. In most perceptual studies, one paradigm is tested and it is usually found that older participants perform worse than younger participants. Implicitly, these results are taken as evidence that there is one aging factor for each individual determining his/her overall performance levels. Here, we show that visual and cognitive functions age differently. We tested 131 older participants (mean age 70 years old) and 108 younger participants (mean age 22 years old) in 14 perceptual tests (including motion perception, contrast and orientation sensitivity, biological motion perception) and in 4 cognitive tasks (MoCA, WCST, verbal fluency and digit span). Young participants performed better than older participants in almost all of the tests. However, within the older participants group, age did not predict performance, i.e., a participant could have good results in biological motion perception but poor results in orientation discrimination. It seems that there is not a single aging factor but many. Meeting abstract presented at VSS 2015.

Ageing and visual spatiotemporal processing

AbstractnAgeing 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 (>60xa0years) 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.

Long-lasting visual integration of form, motion, and color as revealed by visual masking

When two similar visual stimuli are presented in rapid succession at the same location, they fuse. For example, a red and a green disk are perceived as one single yellow disk. Likewise, verniers with opposite offset directions are perceived as one vernier with an almost aligned vernier offset. In fusion, observers have no conscious access to the individual stimuli. Using transcranial magnetic stimulation (TMS), it has been shown that feature fusion for verniers can be modulated for about 400 ms in that either the first or the second vernier dominates the percept, depending on TMS onset. Here, we use light masks to modulate feature fusion for verniers, motion, and color. Our results are similar to the TMS experiment and show that individual visual features are stored for a substantial amount of time before they are integrated.