Sensation

Sensation The process by which our sensory receptors and nervous system receive stimulus from the environment.

Perception The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.

Bottom-up Processing Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”

THE CHT Top-Down Processing Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. THE CHT http://www.psywww.com/intropsych/ch07_cognition/top-down_and_bottom-up_processing.html

Making Sense of Complexity Our sensory and perceptual processes work together to help us sort out complex images.

Failures of perception: cataracts, brain damage Prosopagnosia- complete sensation but incomplete perception. Can sense visual information but cant recognize it—(cannot process top-down) ex: faces

Sensation Our sensory and perceptual processes work together to help us sort out complex processes The Forest Has Eyes is the title of this work---in studying it we look at the expressions on the faces, there is something foreboding about this picture, and after we have read the title we notice other things…

Senses are nature’s gift that suit an organism’s needs. Sensing the World Senses are nature’s gift that suit an organism’s needs. A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice.

What if we could sense everything? Life would hurt. So we can only take in a window of what is out there. This is the study of psychophysics.

Psychophysics A study of the relationship between physical characteristics of stimuli and our psychological experience with them. Physical World Psychological World Light Brightness Sound Volume Pressure Weight Sugar Sweet

22nd October 1850 A relative increase in mental intensity, [Fechner] realized, might be measured in terms of the relative increase in physical energy required to bring it about (Wozniak, 1999). Gustav Fechner (1801-1887)

Detection Absolute Threshold Intensity No No No Yes Yes Detected Observer’s Response Detected Tell when you (the observer) detect the light.

Thresholds Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens) OBJECTIVE 2| Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute thresholds and be influenced by them.

Subliminal Threshold Subliminal Threshold: When stimuli are below one’s absolute threshold for conscious awareness. Kurt Scholz/ Superstock

Difference Threshold Difference Threshold: Minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (JND). Difference Threshold No No Yes Observer’s Response Tell when you (observer) detect a difference in the light.

Weber’s Law The idea that, to perceive a difference between two stimuli, they must differ by a constant percentage; not a constant amount.

Weber’s Law Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I. Stimulus Constant (k) Light 8% Weight 2% Tone 3% LAB

Signal Detection Theory (SDT) Predicts how and when we detect the presence of a faint stimulus (signal) amid background noise (other stimulation). SDT assumes that there is no single absolute threshold and detection depends on: Person’s experience Expectations Motivation Level of fatigue Carol Lee/ Tony Stone Images

SDT Matrix The observer decides whether she hears the tone or not, based on the signal being present or not. This translates into four outcomes. Decision Yes No Signal Present Hit Miss Absent False Alarm Correct Rejection

Sensory Adaptation Diminished sensitivity as a consequence of constant stimulation. OBJECTIVE 3| Describe sensory adaptation, and explain how we benefit from being unaware of changing stimuli. Put a band aid on your arm and after awhile you don’t sense it.

The concept of sensory adaptation applies to all of our senses.

We do not perceive the world how it really is, but as it is useful for us to perceive it.

See page 197 in text for example on difference threshold- 23rd psalm Riddle page 195- bus driver Backmasking: http://jeffmilner.com/backmasking/