Sensation and Sensation and PerceptionPerception

Unit 5 Unit 5

Meyers: Ch. 5,6

Barrons: Ch. 4

Passer/Smith: Ch. 5

Stimulus Detection

• Sensory systems are a means by which the human body interacts with the outside environment.

• Sensory organs capture a certain type of energy. Must be of sufficient quantity to be perceived.

• Energy Types:– Eye: Electromagnetic– Ear: Expanding and compressing molecules of air

(waves)– Nose and Tongue: airborne or substance chemicals– Skin: pressure, temperature, and pain

Sensation1. Stimulus is received by sensory receptors

2. Receptors translate stimulus properties into nerve impulses (transduction)

3. Feature detectors analyze stimulus features

4. Stimulus features are reconstructed into neural representation

5. Neural representation is compared with previously stored information in brain

6. Matching process results in recognition and interpretation of stimulus

Perception

Absolute Threshold

Sensation -> TRANSDUCTION -> Perception

Sense Organ Layman’s Term

Scientist’s Term

Universal Energy Source

Specific Transduction Site

Transduced into What?

Absolute Human Threshold

1

2

3

4

5

6 Vestibular Sense:

Kinesthetic Sense:

Sensory Systems: Transduction

• Visual Sense:

Sensory Systems: Transduction

Sensory Systems: Transduction

Sensory Systems: Transduction

Sensory Processes

• Signal Detection Theory: the point of our ‘detection’ of a stimulus varies depending on a number of factors, including: experience, other environmental stimuli fatigue, expectation, significance of stimulus

• Subliminal Stimuli: Can you learn while you are asleep? Not really… placebo effect has more relevance than sensation. The sensory stimuli are present, but the brain cannot ‘perceive’ it

Difference Threshold

• The point at which the brain has, in fact, perceived a stimuli after the absolute threshold has been met. – Also called the Just Noticeable Difference.– Habituation can cause even higher JNDs: the

brain “gets used to” certain non-threatening environmental stimuli and tunes them out.

Perception

Bottom-up Processing: bringing data from the peripheral nervous system as raw data to the brain

Top-down Processing: what the brain layers

on top of the raw data to create perception

Experience

Other Environmental

Stimuli

Expectations

Knowledge

Etc.

Perception

• Attention: priority is given first to things that are life-threatening, to the exclusion of other stimuli

• Organization and Structure: the brain loves order! It takes millions of pieces of information and makes a “meaningful whole” out of them. Example: Cloud watching

• Illusion: when our perception is incorrect (i.e., the brain’s assembly has arrived at the wrong result)

Perception• Hypothesis Testing: the brain searches for meaning,

looking for similar data in your memories

Perception• Hypothesis Testing: the brain searches for meaning,

looking for similar data in your memories

Perception

• Perceptual Constancies: we cannot attend to everything in our environment. Perceptual constancy keeps certain things constant even as they are changing.

Perception

• Depth Perception: it’s not just an ocular phenomenon, it includes experience and physical maturation– Adding all of it up turns

2-D data into a 3-D image.

Perception of Depth, Distance, and Movement

• Distance Perception: Monocular cues refer to the perception that parallel lines converge as they recede.

Illusions

• An inaccurate perception based on sensory data. Because the data is always incomplete, the brain fills in the holes with experience and expectation.

• Sometimes, it’s wrong.

Experience, Critical Periods, and Perceptual Development

• Perceptual Development: Since the brain draws on experience and expectation (also based on experience), young children often encounter sensory stimuli that the brain does not know how to process. Thus, the brain’s inability to perceive certain things.

• Critical periods are periods during which the brain is ‘primed’ and open to new experience, but after which the brain has moved on and will not be able to perceive.

Restored Sensory Capacity

Taking into account how much the brain relies on experience, and the fact that critical periods limit the brain’s ability to acquire new ways of interpreting data, what would have happened if Helen Keller had undergone surgery to restore her sight as an adult?