Hannah Clare Agnew

Behavioural evidence for distinct mechanisms related to global and biological motion perception

Abstract The perception of human motion is a vital ability in our daily lives. Human movement recognition is often studied using point‐light stimuli in which dots represent the joints of a moving person. Depending on task and stimulus, the local motion of the single dots, and the global form of the stimulus can be used to discriminate point‐light stimuli. Previous studies often measured motion coherence for global motion perception and contrasted it with performance in biological motion perception to assess whether difficulties in biological motion processing are related to more general difficulties with motion processing. However, it is so far unknown as to how performance in global motion tasks relates to the ability to use local motion or global form to discriminate point‐light stimuli. Here, we investigated this relationship in more detail. In Experiment 1, we measured participants’ ability to discriminate the facing direction of point‐light stimuli that contained primarily local motion, global form, or both. In Experiment 2, we embedded point‐light stimuli in noise to assess whether previously found relationships in task performance are related to the ability to detect signal in noise. In both experiments, we also assessed motion coherence thresholds from random‐dot kinematograms. We found relationships between performances for the different biological motion stimuli, but performance for global and biological motion perception was unrelated. These results are in accordance with previous neuroimaging studies that highlighted distinct areas for global and biological motion perception in the dorsal pathway, and indicate that results regarding the relationship between global motion perception and biological motion perception need to be interpreted with caution.

Temporal aspects of natural scene categorisation in healthy ageing

&NA; The visual system has an extraordinary capability to extract categorical information from complex scenes. Age‐related deficits in visual temporal processing have been found with both low‐level and high‐level stimuli. However, it is unknown to which extent those deficits extend to the processing of complex scenes. Here, we investigated the temporal characteristics of natural scene categorisation in healthy ageing. Using a backward masking paradigm, we asked young‐old (aged 59–70), old‐old (aged 70+) and younger adults (18–31 years) to perform a go/no‐go task, in which they had to respond to images of animals whilst ignoring images of landscapes. Both age groups were overall faster and more accurate in responding to the target images as the stimulus onset asynchrony (SOA) between target image and mask increased. Older adults, especially those in the old‐old group, were significantly less accurate than younger adults for short SOAs but performed equally well at long SOAs. However, we found no age‐difference in reaction times. Our findings suggest that the temporal processing of complex scenes is impaired in healthy older adults independently of reduced motor abilities. They also indicate that such deficits in natural scene categorisation become more evident with increasing age. Our findings might have important implications for the wellbeing of older adults and road safety in general. HighlightsWe used a backwards masking paradigm in a go/no‐go categorisation task.Younger and older adults responded to animal images, but ignored landscape images.Older adults were less accurate for short SOAs only, compared to younger adults.There were no age‐differences in reaction times.Our results are unlikely to be driven by reduced motor abilities.Temporal processing of complex natural scenes is impaired in healthy older adults.