Sensation and Perception

1. Sensation and Perception

2. A word on where we’re at in this point in the syllabus: • We have just finished covering five different approaches to understanding human personality & behavior (Freudian, Humanistic, Behavioral, Biological & Cultural/Systemic). • This coming Monday and Wednesday we will be talking about the fifth and final approach, the Cognitive Approach.

3. The Cognitive Approach emphasizes that people are shaped (& differ from each other) because their perceptions & their thought processes differ. So understanding some background information on how we perceive things in our environment may help assist us in our understanding of the Cognitive approach. That is why we are now turning our attention to the topic of “Sensation & Perception,” a specialty area within Psychology that works at understanding how our senses work & how we perceive stimuli in the environment. So, with no further delay….

4. 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.

5. 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.

6. 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!

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

8. 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.

9. The Retina • Network of neurons on rear surface inside the eye

10. 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

11. 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”!

12. The process of “transduction” in vision. Work at figuring out the answers to these questions. We will be discussing them in class. • 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?

13. 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.)

14. Our textbook author writes: • “The whole process [of vision] is as complex as taking a car apart, piece by piece, transporting it to a different location, then having specialized workers reconstruct it.” p. 159 • Work at understanding what this quote is saying about vision. The quote refers to parallel processing & to feature detectors--discussed in your textbook on p. 157-158

15. 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. • “…perceptions arise from the interaction of many neuron systems, each performing a simple task.” p. 152 (148)

16. 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?

17. Perception goes “right” more times than when it goes “wrong.” The times it “goes wrong” however, can provide us with impt. info on how perceptions works! From your reading, what examples of this did you find? Maybe you found some of these…. Figure and ground Perceptual constancies (shape and size constancy) Size-distance relationship The Ames room (Fig 13.12)—how does this work? Closure Context effects Perception goes beyond vision.It involves what we see.

18. Schemas and Perceptual Set

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

20. 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

21. We’ll be talking about each of these more in class, but be thinking of whether you might have examples of how each of these have shaped YOUR perceptual sets at particular times in your life! • Context effects • Past experiences • Effects of our culture

22. 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.

23. 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!

24. We’ll be doing some exercises in class to work at better understanding how our schemas work! Until then, work at practicing “seeing people” through cognitive lenses by noticing how people sometimes perceive the same situation in different ways!