 Hi, I'm Kevin Eung and I'll be presenting our work on the relationship between tactile intensity perception and afference spike count. When we deliver a sinusoidal vibration on the skin, the perceived magnitude or intensity smoothly increases as a function of amplitude. However, the response of a single sensory afferent has several entrainment plateaus, where the afferent fires one-to-one or two-to-one for each cycle or vibration over a range of amplitudes. Afference can also be entrained across frequencies. By increasing the spatial frequency, for example with smoother textures, would proportionately increase the discharge rate. But that doesn't necessarily lead to a more intense sensation. There are several proposed models for coding intensity perception. One of the more recent models is based on the total spike activity across all afferents, weighted by afferent type. For example, the highly sensitive perchinian afference might be weighted less than the slowly adapting afference. But what has made it difficult to study the relationship between spikes and perception is that the use of sinusoidal stimulation results in a complex population response. For instance, changing the frequency of the vibration changes the activated afferent type as there are different preferred frequencies. To control and investigate the number of spikes generated in the same population of afference, we developed a new experimental approach based on mechanical impulses so brief that there is only time for one spike per pulse to be evoked. The number of spikes evoked in afference is controlled by the repetition rate. Unlike sinusoidal stimuli with different frequencies, impulses are identical and thus activate the same population and also the same type of afference, regardless of the repetition rate. We delivered these impulses out of stimuli using a probe attached to a mechanical shaker. Subjects had to rate the magnitude of pulse strains between 20 and 200 Hz, against the standard which was the 100 Hz pulse strain. We tested three different stimulation amplitudes which would recruit a different combination of afferent types. Our results showed that perceived intensity increased when the repetition rate of the stimuli and the spike rate within the same population of afference increased from 20 and 100 Hz, which then plateaued beyond this point. These effects did not appear to be sensitive to the mix of afferent types that were recruited, as the same trend was observed at different amplitudes. Electric of stimulation, which activates afference non-selectively, had similar results but not in all subjects. Thus, we see that the relationship between intensity and the number of spikes is also moderated by the frequency. Below 100 Hz, the number of spikes in their population directly affects intensity, whereas above 100 Hz, this became minimal. This could be why fine textures which evoke high frequency vibrations in the skin do not feel disproportionately intense as the way that red model would predict. Furthermore, the use of pulse rate render intensity perception, in the case of neural interfaces, has its limitations.