Overall, our findings illustrate that physiological aging predominantly affects those tasks that are processed at the lower levels of the motion pathway, including D
min, contrast, and speed. This is also supported by the higher correlational values obtained between these tasks. The initial stages of motion processing rely on detecting changes in the position of objects over time (
Adelson & Bergen, 1985), which is also related to the perception of speed. The changes at these low levels of processing might be explained by aging changes in older adults, such as changes in optical quality and/or neural declines at either a retinal level or in cortical area V1. Despite the observed changes to the processing of the initial inputs to motion perception, we did not find an age effect on two tasks that require the integration of local motion signals: the perception of translational and radial global motion. Similar to newer evidence by
Shaqiri et al. (2019), our correlational analysis did not show statistically significant relationships between the three more complex motion tasks (translational and radial global motion coherence, and biological motion), implying that mechanistically, the perception of these complex patterns does not rely directly on lower levels of processing. For example, small deficits in the perception of individual components of the RDK stimuli may not impact on the determination of overall global motion coherence. Motion coherence thresholds have also been shown to be quite robust to blur (
Zwicker, Hoag, Edwards, Boden, & Giaschi, 2006). An additional explanation for the preserved global motion perception in older adults relates to the existence of higher-level mechanisms that have the potential to compensate for local deficits. For instance, in a recent study using imaging techniques,
Biehl, Andersen, Waiter, and Pilz (2017) reported that older adults have additional activation of frontal areas when perceiving global motion patterns (particularly radial). Aside from motion, there is evidence from neurophysiological and imaging studies of additional activation of frontal regions in older adults to compensate some features of visual function, such as visual attention and object recognition (
Cabeza et al., 2004;
Davis, Dennis, Daselaar, Fleck, & Cabeza, 2008), as well as audio-visual integration (
Chan, Pianta, Bode, & McKendrick, 2017). Overall, our findings indicate that integrative processes presumed to operate in global motion tasks are intact in older adults, at least for the speeds of dot motion used in our experiments.