Sensation and Perception Sensory input and Psychophysics

Sensation and Perception What do you hear? What do you see? What do you taste? What do you smell? What do you feel? (not emotion) What conclusions can you draw from these answers?

Sensation Starts with a stimulus (any aspect of change in our environment to which we respond) Can be measured in size, duration, intensity and wavelength Occurs anytime a stimulus activates a receptor

Sensory Receptor Living cell that responds to certain type of energy Often located in sense organs Specialized structure that collects energy particularly well… (eye, ear, etc) Detect physical changes in energy such as heat, light, sound, and physical pressure

Eye- notes changes in light

Ear- notes changes in sound

Skin- notes changes in heat and pressure

Perception Organization of sensory information into a meaningful experience Comes from a combination of sensations and past experiences

Psychophysics The interaction between the physical world (stimuli) and the psychological world (internal experience) What is the relationship between color and wavelength? How does changing a light’s intensity affect your perception of it’s brightness?

Threshold How much energy is required for someone to hear a sound, or see a light? How much of a scent must be in a room for someone to smell it? How much pressure must be put on the skin for someone to feel it? Is it the same for everyone?

How strong must a stimulus be in order for detection? Threshold- dividing line Not exact Absolute threshold- point at which a very weak stimulus can be detected 50% of the time Difference threshold- smallest change a person can detect 50% of the time. (JND) just noticeable difference

Weber’s Law The larger the magnitude of the stimulus, the larger the JND 25 watt light bulb / 50 watt light bulb very different 175 watt light bulb / 200 watt light bulb hard to notice

Weber’s Law The JND increases in direct proportion to the intensity of the stimulus. Often not true when stimuli approach extreme values.

Fechner’s Law Accounts for the extreme values exception Can be demonstrated in a curve Follows a logarithmic relationship The curve drops as the magnitude of the stimulus approaches extreme values

Fechner’s Law Exceptions include electric shock and heaviness

Sensory adaptation Our senses are tuned to change and respond to increases and decreases in stimuli, or new events rather than constant stimulation. We adapt to change/deviation in stimulation Movie theater Clothes on body

Signal Detection theory Study of people’s tendencies to make correct judgments in detecting the presence of stimuli Recognizing stimuli against a competing background of stimuli Individuals vary based on situation Preattentive process-getting info automatically when presented Attentive process- paying attention to only one of the stimuli at a time when presented with multiple stimuli p 213

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