Week 6 (21 – 25 Nov): Perception

This has been a busy week. Much busier than I had anticipated, but not too busy that I haven’t had time to think about perception. The biggest problem with this section is that it has so many little perception rules that it seems unruly. Thus, the visual notes, the two assignments, and other ways of organizing the information.


Image via Wikipedia

One of my favorite things about the unit is that it is so accessible in our daily life. Nearly every time you travel through traffic, you can identify perceptual laws. And, if you are out at night, you can see how they can go awry. For example, I was running the other night and on that dark stretch in Phu My Hung over by the Korean International School, I saw a car coming towards me. I was momentarily alarmed when I saw that its right headlight had come unattached and was heading right for me! The car seemed to be literally expanding right before my eyes. Then, I saw that it was simply two motorcycles whose headlights had traveled more or less at the same height for several meters giving the illusion that they were joined: law of common fate, law of proximity.

But also their sizes and heights acted as cues. Two objects that are the same size are seen as being the same distance while a smaller object is perceived as farther away than a larger object. Two objects that are the same height from the horizon, or in my case just the same height since there is no horizon at night, seem to be the same size while an object closer to the horizon is perceived as farther away. Thus the two headlights seemed to be the same distance and thus strengthened the impression of their proximity and their common fate.

In addition, top-down processing suggested that two headlights would be from a car. Of course, where I’m from there are more cars than motorbikes, so I wonder if it would be the same for y’all coming from a land of many motorbikes and few cars. Perhaps that is something to blog about or comment on.

Binocular depth perception cues are much more difficult to have casual experiences of; you have to do things to give yourself the experience. For example, look at something and close one eye and then the other and watch how it jumps back and forth. If you can get closer then you can compare the degree of jump as you close each of your eyes. This would be a demonstration of binocular disparity. Is this top-down or bottom-up processing? Again, comment or blog.



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.