Chapter 3: Sensation and Perception

The sense organs contain sensory receptors help in transmission of sensory information to the central nervous system.

Stimulus energy	Sense organ	Sense
Light	Eyes	Vision
Vibration of sound	Ears	Hearing
Chemical substances	Tongue/ Nose	Taste/ Smell
Pressure/ Temperature	Skin	Touch

Sensation and Perception

Sense: A system - translate data - outside nervous system – into neural activity.

Sensations: Raw data of senses.

Perception: Interpretation of raw information – give meaning – knowledge, experience,
understanding.

Absolute Threshold

·         Minimum amount of energy necessary for a sensation to occur.

·         The point which distinguishes between ‘something” and “nothing”.

Difference Threshold

·         Just Noticeable Difference, j.n.d.

·         Minimum detectable difference between two similar stimuli that is detectable 50% of the time.

Transduction

·         Sensory receptors convert the sensory stimulation into neural impulses.

Sensory Adaptation vs Habituation

Adaptation: - Decrease in response to a continuous stimulus.

Two possible explanations:

- Sensory receptors no longer sends signals to the brain.

- The thalamus has filtered out the ongoing stimulus.

e.g.: We have adapted the temperature of the water after a brief time in swimming pool.

Habituation: - Stop attending to a constant, unchanging stimulus after repeated presentations.

e.g.: The noise of the air in your classroom. Initially, you will get distracted. Over time, you pay less attention to the it and eventually your response to the noise will diminish.

Light Adaptation
·         Dark adaptation: - Pupils dilate to allow more light to enter the eyes when you are in a darker environment after exposure to bright light.
·         Light adaptation: - Pupils constrict so that less light enters the eyes when you are in a brighter environment after exposure to darkness.

Afterimages

·         Persistent sensations of original picture followed by perception of the complementary (opponent- process theory) or optical illusions appear after the exposure to the picture has ceased.

Jesus illusion

Stare at the four black dots in the centre of the image for 30 - 60 seconds. Then close your eyes or look at the white-coloured wall). You should see a white circle with an image (people called it ‘Jesus’) inside it.

Different aspects of vision

Cones-    Most densely packed in centre of retina (fovea)

-          Provide colour vision & fine details

-          Sharpness of vision

Rods  -     Provide vision in black and white and shades of grey

-          More sensitive to dim light than cones.

Colour blindness: - caused by defective cones

Three types of colour blindness:

 - Red-green colour blindness (see blues, yellows, shades of grey)

 -  Blue-yellow colour blindness (see reds, greens, shades of grey)

 -  Monochrome colour blindness (see only shades of grey) – is rare.

Theories of Color

Trichromatic Theory: 
- Three types of cones and sensitive to red, green, or blue respectively.

Opponent-Process Theory: 
- Three independent receptor types which all have arranged in pairs: white-black, blue-yellow and red-green.

Visual Perception

·         Process used to organize sensory impressions caused by the light that strikes our eyes.

·         An active process – involves experience, expectations and motivations.

Perceptual Organization

·         Figure-ground perception

“Elements are perceived as either figure or ground.”

Figure : The element in focus.

Ground: The background.

Gestalt Rules for Perceptual Organization

 “The whole is other than the sum of the parts.”— Kurt Koffka

-This quote is Gestalt Theory in a nutshell. We see the entirety as more than the sum of the individual objects, and even when the parts are wholly separate entities.

- Certain properties of stimuli lead us to group them together more or less automatically.

Rules for grouping stimuli together:

-          Proximity (nearness)       -          Connectedness

-          Similarity                          -          Closure

-          Continuity

How do we transform 2D objects to 3D perception?

Binocular cues- depth clues from both eyes together.

·         Retinal/ binocular disparity

·         Convergence

Monocular cues- depth clues from a single eye.

·         Motion parallax

·         Accommodation

·         Pictorial depth cues

Depth perception is the ability to perceive distance and see the world in 3D.
There are many things that we use to judge how far away an object is. 

Some of the cues that you need only one eyes to see them. 

Hence, they are referred as monocular cues and they are:

-          Relative height

-          Relative size

-          Interposition

-          Accommodation

-          Linear perspective

-          Texture perspective

-          Relative clarity

-by Zhi Zhong