increase the firing rate of individual primary afferent fibres by increasing the size of the receptor potential
most common way to do this is by increasing the size of the receptive field stimulated
2. POPULATION CODING :
increase the number of primary afferent fibres responding
this process is called RECRUITMENT
recruited fibres will not respond equally
because of frequency coding, the primary afferent whose receptive field is in the centre of the point of stimulation (i.e. the green fibre) will respond with the largest number of action potentials
this concept is critical with respect to understanding lateral inhibition
Stimulus Intensity 
2. POPULATION CODING :