Sensation and Perception

Let’s begin with some basic definitions… Sense – physical system that receives physical stimulation from surrounding environment and translates that stimulation into an electrochemical message Sensation – detecting physical energy in environment and encoding it as neural signals. Neurons transmit the information from the sense organ to the brain. Perception – processing of information done by the brain – mental processes that organize and interpret sensory information that has been transmitted to the brain.

Transduction Communication between the brain & the rest of the body (& between different regions of the brain) occurs via neuron. We recently learned how communication between neurons occurs electrochemically (within neurons: electrical; between neurons: chemical). So the brain’s “language” is electrochemical! All senses involve something called receptor cells. Their job is to transduce (transform or even “translate”) physical stimulation/physical energy from the environment into electrochemical messages that can be understood by the brain.

So where do vision and hearing (& the other senses) happen? The Brain! The physical energy in the environment is detected by the eyes, ears, etc. but we can’t see, hear, etc. until the brain interprets them—i.e., makes sense of them. So in a way, we see, hear, smell, etc. in our brains!

Learning about the eye… Cornea – transparent membrane covering the front of the eye (protective) – the light enters the eye through the cornea Pupil – small adjustable opening – regulates the amount of light entering the eye

Iris – muscle which surrounds the pupil and controls the size of the pupil; at largest dilation (opening), pupil is 17 times larger than the smallest dilation (opening). Lens – focuses incoming rays on back surface of the eye (retina) - elastic, muscles stretch or thicken (thus changing the curvature of the lens) to bend the light at the right angle (so light is focused on retina, depending upon distance of object) this is called accommodation.

The Retina Network of neurons on rear surface inside the eye

Sensory Receptor Cells There are two types of sensory receptor cells which are located on the retina Rods Cones Rods enable us to see black and white, are more sensitive to light, and there are 100 million in each eye Cones enable us to see color, they work best in bright light, there are 6.5 million in each eye and they are located mostly at the center of the eye

More on Sensory Receptor Cells These cells transform light energy into neural impulses that are sent to various areas in the brain through the bundle of neurons called the optic nerve. What is the place called in which the optic nerve leaves the eye? The blind spot Why is it called “the blind spot”? Because there are no rods & cones on this area (there are neurons instead), images that fall on this area of the retina are not “seen”! http://www.blindspottest.com/

Review Questions What are the receptor cells of vision?  What physical stimuli in the environment are they detecting/responding to?  How does the physical stimuli get to the receptor cells?  What do the receptor cells then “do” with the physical stimuli?

What is parallel processing? This occurs when different aspects of the scene (e.g., color, movement, etc) are broken down and processed by different regions of the brain then integrated together to form a whole. (Thus people with specific brain damage will sometimes lose their ability to perceive one aspect of visual stimulation, but not others.)

Parallel processing is the ability of the brain to simultaneously process incoming stimuli of differing quality. This becomes most important in vision, as the brain divides what it sees into four components: color, motion, shape, and depth. These are individually analyzed and then compared to stored memories, which helps the brain identify what you are viewing. The brain then combines all of these into one image that you see and comprehend. Parallel processing has been linked, by some experimental psychologists, to the Stroop effect. This is a continual and seamless operation. http://faculty.washington.edu/chudler/java/ready.html

The mystery of feature detectors… Feature detectors are cortical neurons that respond to specific features of a scene (e.g., particular edges, lines, angles and movements) The brain then needs to assemble the whole image from these specific features.

How we see color… Based on the wavelength of light the object reflects rather than absorbs. Thus if an object absorbs every color of light except red, then the object reflects red and therefore we see red. Color is also based on interpretation of context. Is the red I see the same red you see?

We have three types of cones We have three types of cones. If you look at the graph below, you can see each cone is able to detect a range of colors, but at lower sensitivity. Even though each cone is most sensitive to a specific color of light they also can detect other colors.  In addition,  they overlap each other. The overlap allows use to see many different colors. The three types of cones are commonly labeled by the color they are most sensitive (blue, green and red). The color yellow results from green and red cones being stimulated while the blue cones have no stimulation. http://colorvisiontesting.com/online%20test.htm

A perceptual set is… “a mental predisposition to perceive one thing and not another” This is based on experiences, assumptions and expectations.

What shapes our perceptual sets? What things do you think might affect our perceptual sets (i.e., our tendency to perceive things in certain ways)? Context effects Past experiences Effects of our culture

Schemas Another word used to describe perceptual set is schemas. Schemas can influence our perception because we tend to see things that we expect to see. We interpret things based on similar things we have experienced in the past –this is called assimilation.  Schemas can be useful, because they allow us to take shortcuts in interpreting a vast amount of information. However, schemas can contribute to stereotypes and make it difficult to retain new information that does not conform to our established schemas.

Schemas….. Now what do you think would happen if we receive new information that doesn’t not fit our schemas? When we receive new information we can ignore it (!) or we can change our schemas to fit the new information. This is called accommodation. Schemas are almost like a box that we put information into. The way we organize compartments in the box is based on things like our past experiences, contexts, etc. and this influences our perceptions!

What is a crib? For example, suppose you were in a conversation and someone used the word "Speed", what would you think they meant? Could it be: the rate at which you move (distance/time) going faster than the speed limit the film with Keanu Reeves and Sandra Bullock the drug Gary Speed, the Welsh footballer