Looking at the electrical responses from single neurons, Romo and his colleagues determined that, if all the neuronal firings were treated equally, these responses could not explain the monkeys' perception of the signal. If the researchers assumed that the monkeys paid more attention to the beginning of the response, however, the neural activity perfectly explained the monkeys' errors when judging different durations of stimuli.
Romo suggested that the best explanation for the behavioral data was to assume that the monkeys pay the most attention to the first 250 milliseconds of neural firing, and that their attention falls off exponentially from there. The longer the stimulus, the less important additional neuronal firings become to the monkeys' perception of how fast the stimulus is vibrating, even though they continue to pay some attention throughout.
Figuring out how the brain codes sensory information into neuronal firing and how the firing patterns are interpreted by perceptual areas of the brain is a huge challenge in neurophysiology, one that's often overlooked, said Romo.
"The neuronal correlates reported in most of the neurophysiological studies in the different sensory modalities simply do not pay attention to this," he noted. "They assume that variation in firing rate is enough as a measure."