Role of task difficulty in modulation of neural activity

How does attentional modulation of a neuron’s preferred feature (μ), or changing its tuning width (σ), or its response gain (g) benefit behavioral performance? We investigate this in the context of a visual search task, e.g., search for a vertical bar among horizontal bars (which becomes more difficult as the target orientation approaches horizontal). We consider SNR (ratio of expected population response to the target over the distractor) as the performance metric [1]. We compute the benefit in performance per unit change in μ, σ and g. Our simulation results show that changing σ can be beneficial or not, depending on the task difficulty due to target-distractor discriminability (measured here as separation in degrees between target and distractor orientation). We find that a unit change in σ is more beneficial in difficult than easy tasks (fig 1b). A similar trend is observed for changing μ (fig 1a). However, the opposite trend is observed for gain modulation – a unit change in g is more beneficial in easy tasks than difficult tasks (fig 1c).