Decision making is a ubiquitous cognitive process that determines choice behaviour. In recent years there has been increased interest in how information about multiple discrete sensory events are combined in support of single, integrated decisions. Previous studies have shown that integrative decision-making is biased in favour of more reliable stimuli. As reliability-weighted integration typically mimics statistically optimal integration, it remains unclear whether reliability biases are automatic or strategic. To dissociate reliability-weighting and optimal decisions, we developed a task that required participants to monitor two successive epochs containing brief, suprathreshold coherent motion signals which varied in their reliability. Rather than judging the individual target motion directions, however, participants had to reproduce the average motion direction of the two targets. Using mixture distribution modelling and linear regression to model behavioural data, we found robust biases in favour of the more reliable stimulus, despite the fact that unbiased responses were optimal in our paradigm. Using population-tuning modelling to characterise feature specific brain activity recorded using electroencephalography, we observed robust and sustained feature-specific responses to target signals in both epochs. Using the same method, we were able to capture the temporal dynamics of integrated decision-making by characterising tuning to the average motion direction. Critically, the tuning profiles to the average motion direction exhibited biases in favour of the more reliable signal, in keeping with the modelled behavioural responses. Taken together, our findings reveal that temporal integration of discrete sensory events is automatically and suboptimally weighted according to stimulus reliability.