Sensation

Sensation is the process by which we RECEIVE information from the ENVIRONMENT and encode it as neural signals. 1. Involves coordination of RECEPTORS, NEURAL PATHWAYS, and SENSORY PROCESSES. 2. These sensory systems are tied to PERCEPTION.

Perception is the process of SELECTING and INTERPRETING information from the ENVIRONMENT. Psychophysics is the study of the relationship between physical ENERGY and psychological EXPERIENCE. Physical World Psychological World Light Brightness Sound Volume Pressure Weight Sugar Sweet

Bottom-up processing is the sensory analysis that starts at the ENTRY level (start with the sensory receptors and work up to a higher level.) Top-down processing is constructing perceptions drawing both on sensations coming BOTTOM-UP and on our EXPERIENCES and expectations. THE CHT

Our sensory and perceptual processes work together to help us sort out complex images. “The Forest Has Eyes” by Doolittle

Thresholds GUSTAV FECHNER was the first person to study the relationship between stimulus intensity and sensation intensity and realize a relative increase in mental intensity might be measured in terms of a relative increase in physical energy required to bring it about. 10/22/1850

Absolute threshold by Fechner 1. the point at which a stimulus can be detected 50% of the time 2. the MINIMUM amount of stimulation needed to detect a stimulus

Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens)

Signal detection theory states that there is no actual absolute threshold because the threshold CHANGES with a variety of factors such as attention, fatigue, expectations, motivation, and alertness. Subliminal stimulation is the receipt of messages that are BELOW one’s absolute threshold for conscious awareness. They have a momentary subtle effect on thinking.

http://www. youtube. com/watch http://www.youtube.com/watch?v=RxIEt-Wq6ME&safety_mode=true&persist_safety_mode=1&safe=active Start at 1:07 Stop at 2:30

Difference Threshold 1. A change between two stimuli that can be detected 50% of the time 2. Also called “JUST NOTICEABLE DIFFERENCE” or JND Difference Threshold No No Yes Observer’s Response Tell when you (observer) detect a difference in the light.

Weber’s Law ERNEST WEBER experimented with JND and discovered WEBER’S LAW Two stimuli must differ by a constant minimum percentage (rather than a constant amount) to be perceived as different.

Receptors A. Environmental information exists in many forms 1. Air vibrations, GASES, CHEMICALS 2. The body receives these forms through special cells a. Receptor cells act as TRANSDUCERS converting one form of energy into another b. example: TASTE BUDS convert chemical signals to a pattern of electrochemical activity sent to the brain

B. Receptor sensitivity is sensitive to CHANGE. 1. Sensory adaptation a. a weakened sensitivity due to PROLONGED stimulation b. example: you notice a bad smell as you first enter a room, yet the smell seems to abate after a time or you feel a band aid when first put on then you don’t notice it anymore

2. Habituation a. a decline in the sensory sensitivity at the neural level due to REPEATED stimulation b. Different from sensory adaptation in that responsiveness can reappear if stimulation level is increased or decreased