Age-associated delay in mental rotation

Age-associated slowing in mental rotation (MR) process has been documented in the literature. Particularly, the intercept of the response times (RTs) function of rotation angle has been consistently found to be larger in older than in younger adults. However, the intercept represents the speed of response in two distinct sub-processes of MR: the initial phase of stimulus encoding and the final phase of response selection and execution. Thus, it remains unclear which of these two sub-processes of MR is affected by age. To investigate this, we recorded event-related potentials in younger and older individuals during a letter rotation task. The onset of the rotation-related negativity (RRN), the electrophysiological correlate of MR, was delayed in older (n = 20; mean age = 20.1) as compared to younger participants (n = 20, mean age = 73.4). Consistent with this observation, additional analyses revealed that the RRN amplitude was modulated by rotation angle between 350 and 500 ms post-stimulus in younger adults (n = 26, mean age = 21.0), while this modulation only emerged in the later time window (500-650ms) in older participants (n = 26; mean age = 73.6). These results suggest that MR occurs later in older adults and demonstrate that the initial phase before MR proper is one source of the age-related slowing observed in MR tasks. Possible accounts for this age-associated delay include a prolonged phase of stimulus encoding and/or selective difficulties in directing attention away from the external stimulus towards its internal mental representation.