Objectives Chapter 1, Part 1 Illustrate and describe the perceptual cycle Explain the difference between top-down and bottom-up processing Compare and contrast psychophysical and physiological approaches to studying perceptual processes

Why Study Perception? Understanding how you perceive the world –Language processing –Color vision –Depth perception Future careers in Research –Multitasking - Driving and cell Phones –Optimizing Computer Monitor Displays Medical applications –Assisting people with vision and hearing losses by understanding their needs

Shall we play a game?

Perception is cyclical. It never ends!

The Perceptual Process - continued Transduction –Change from environmental energy to electrical energy in the nervous system Neural processing –Interconnected neurons that propagate the electrical signal from receptor cells throughout the brain

Two Interacting Aspects of Perception Bottom-up processing –Processing based on incoming stimuli from the environment –Also called data-based processing Top-down processing –Processing based on the perceiver’s previous knowledge –Also called knowledge-based processing

Approaches to the Study of Perception Levels of Analysis –Observing perceptual processes at different scales Psychophysical level - the stimulus- perception relationship (Line A) Physiological level - the stimulus- physiology relationship (Line B) –These levels are interconnected, but we usually have to focus on specific parts in controlled experiments

Objectives Chapter 1, Part 2 Define psychophysics. Describe ways to measure perception. Explain mental processes with mathematical laws. Compare and contrast Absolute Threshold and Difference Threshold.

Psychophysics - Qualitative Methods Description –Basic description of what a person perceives –First step in studying perception –Called phenomenological method Recognition –Categorization of stimuli

Psychophysics - Quantitative Methods Absolute threshold - smallest amount of energy needed to detect a stimulus –Method of limits Stimuli of different intensities presented in ascending and descending order Observer responds to whether she perceived the stimulus Cross-over point is the threshold

Quantitative Methods - continued Absolute threshold (cont.) –Method of adjustment Stimulus intensity is adjusted continuously until observer detects it Repeated trials averaged for threshold

Quantitative Methods - continued Absolute threshold (cont.) –Method of constant stimuli 5 to 9 stimuli of different intensities are presented in random order Multiple trials are presented Threshold is the intensity that results in detection in 50% of trials

Method of Constant Stimuli

Quantitative Methods - continued Difference Threshold (DL) - smallest difference between two stimuli a person can detect –Same methods can be used as for absolute threshold –As magnitude of stimulus increases, so does DL –Weber’s Law explains this relationship DL / S = K

Table 1.3 Weber fractions for a number of different sensory dimensions

Quantitative Methods - continued Magnitude estimation –Stimuli are above threshold –Observer is given a standard stimulus and a value for its intensity –Observer compares the standard stimulus to test stimuli by assigning numbers relative to the standard

Quantitative Methods - continued Magnitude estimation (cont.) –Response compression As intensity increases, the perceived magnitude increases more slowly than the intensity –Response expansion As intensity increases, the perceived magnitude increases more quickly than the intensity

Actual Intensity of the stimulus. What it “seems’ like to you.

Quantitative Methods - continued Magnitude estimation (cont.) –Relationship between intensity and perceived magnitude is a power function –Steven’s Power Law P = KS n

Other Measurement Methods Searching for stimuli –Visual search - observers look for one stimulus in a set of many stimuli and compares it to stored data (memory) Reaction time (RT) - time from presentation of stimulus to observer’s response is measured

Objectives Chapter 1, Part 2 Define psychophysics. Describe ways to measure perception. Explain mental processes with mathematical laws. –Weber’s law –Steven’s Power Law Compare and contrast Absolute Threshold and Difference Threshold. Reading2 and 3 (synesthesia: Hard-Wired or Learned?) –What impact would synesthesia have on visual search?