Myers' Psychology Unit 4: Sensation and Perception

How does the eye transform light energy into neural messages?

After entering the eye and being focused by a lens, light-energy particles strike the eye's inner surface, the retina. The retina's light-sensitive rods and color-sensitive cones convert the light energy into neural impulses which, after processing by bipolar and ganglion cells, travel through the optic nerve to the brain.

What is the energy that we see as visible light?

Each sense receives stimulation, transforms (transduces) it into neural signals, and sends these neural messages to the brain. In vision, the signals consist of light-energy particles from a thin slice of the broad spectrum of electromagnetic energy. The hue we perceive in a light depends on its wavelength, and its brightness depends on its intensity.

How does the brain process visual information?

Impulses travel along the optic nerve, to the thalamus, and on to the visual cortex. In the visual cortex, feature detectors respond to specific features of the visual stimulus.

What are the absolute and difference thresholds, and do stimuli below the absolute threshold have any influence?

Our absolute threshold for any stimulus is the minimum stimulation necessary for us to be consciously aware of it 50 percent of the time. Signal detection theory demonstrates that individual absolute thresholds vary, depending on the strength of the signal and also on our experience, expectations, motivation, and alertness. Our difference threshold (also called just noticeable difference, or JND) is the barely noticable difference we discern between two stimuli 50 percent of the time. Priming shows that we can process some information from stimuli below our absolute threshold for conscious awareness. But the effect is too fleeting to enable people to exploit us with subliminal messages. Weber's law states that two stimuli must differ by a constant proportion to be perceived as different.

What are sensation and perception? What do we mean by bottom-up processing and top-down processing?

Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. Perception is the process of organizing and interpreting this information. Although we view sensation and perception separately to analyze and discuss them, they are actually parts of one continuous process. Bottom-up processing is sensory analysis that begins at the entry level, with information flowing from the sensory receptors to the brain. Top-down processing is analysis that begins with the brain and flows down, filtering information, through our experience and expectations to produce perceptions.

What is the function of sensory adaptation ?

Sensory adaptation (our diminished sensitivity to constant or routine odors, sounds, and touches) focuses our attention on informative changes in our environment.

How are we affected by selective attention?

We selectively attend to, and process, a very limited aspect of incoming information, blocking out most, often shifting the spotlight of our attention from one thing to another. We even display inattentional blindness to events and changes in our visual world.