Week 4 (7 – 11 Nov): From Stimulus 2 Perception

As I study the material in the textbook & read from other sources I continue to marvel at the lack of clarity between the four basic steps in process of transforming stimuli to perceptions:

Stimulus –> Transduction –> Sensation –> Perception

Stimulus is easy, right? That is the energy & substances & objects in our environment that we encounter and that match up with the receptor cells in our sense organs. Stimuli clear exist in the environment and outside of our nervous system.

Transduction, on the other hand, is where things get murky, but only just. Transduction, we are told, occurs when the receptor cells transform the stimuli into neural impulses. Again, it takes place in our sense organs, but outside of our nervous system… or does it? It ends with the firing of the nerve cell that is designed to be stimulated by the stimulus.

Sensation, though, is definitely steeped in murkiness. The textbook defines sensation as “the process by which stimulation of a sensory receptor produces neural impulses that the brain interprets…” But isn’t the production of a nerve impulse from transduction? When is the nerve impulse part of transduction and when is it part of sensation. The boundary is not clear to me. Are the receptor cells transducers of stimuli or are they sensors of stimuli? Is this just semantics? Will it make a difference on the AP exam?

Perception is definitely the murkiest! Perception is the process of making sensory patterns meaningful. That sounds pretty straightforward, right? I mean we interpret the patterns in the brain, but we’ve completed the brain unit so we can ask where in the brain is the boundary between sensation & perception. Aaah! MURK! Is the thalamus, that great relay station of sensory input, part of sensation or is it perception? Is the initial evaluation in the cerebral cortex sensation or perception. Is it only when other parts of the association cortex are involved that it becomes perception?

I’m definitely more comfortable when these things are clearly defined and delineated. Perhaps one reason there is this excessive amount of murk in this area is that psychologists & neurologists and their endless variations and allied fields are not yet sure.

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