When more equals less: overtraining inhibits perceptual learning owing to lack of wakeful consolidation

Abstract

Performance on perceptual tasks usually improves with training. However, too much consecutive training can be detrimental. Repeated within-day testing or overtraining demonstrates the detrimental effects this has on perceptual learning. Consolidation of learnt information during sleep has the power to prevent such deficits in learning. However, little is known regarding the role of wakeful consolidation in preventing the effects of overtraining. Here, we report that perceptual deterioration may result from the disruption of early wakeful consolidation processes. Three groups were tested on day 1 and again 24 h later, on a motion discrimination task. Participants who had a 1 h break between the two training sessions on the first day displayed improved accuracy on the second day (i.e. learning). Subjects who only completed the first training session on day 1 also exhibited learning. However, individuals who completed two blocks without a break ('overtraining') showed no improvement in accuracy on day 2. Interestingly, changes in reaction times were not susceptible to the effects of overtraining, but instead speeded up as a function of total performed trials. These data suggest that effects of overtraining might be due to disruption of wakeful consolidation processes.

Figure 1.

Learning effects for accuracy and reaction times. (a–c) Solid lines show accuracy (% correct) for session 1 day 1, dashed lines show data for day 2. (d–f) Solid lines show normalized reaction times for session 1 day 1 dashed lines show data for day 2. (a,d) Control: subjects training for one session on day 1. (b,e) Overtraining condition: subjects training for two consecutive sessions on day 1. (c,f) Delay condition: same as overtraining condition except a 1 h delay was introduced between the two sessions on day 1. All error bars show ± s.e. of the mean.

Figure 2.

Accuracy and reaction time changes across trials. Solid vertical lines represent the period of time during which sleep occurred. (a–c) Accuracy (% correct) and (d–f) normalized reaction times as a function of trial number averaged across coherence levels. (a,d) Control: subjects performed only one session on day 1. (b,e) Overtraining condition: subjects performed two consecutive sessions on day 1. (c,f) Delay condition: subjects performed two sessions on day 1, separated by a 1 h delay (represented by dashed vertical lines). All error bars show ± s.e. of the mean. The asterisk over the second session in (c) indicates a positive linear trend, whereas the ‘n.s.’ over the second session in (b) indicates a non-significant linear trend.