SensationIntro. to PsychologyPSY-101Instructor: Ms. Tahira Zafar

Sensation and Perception

Sensation The process through which the senses pick up visual,

auditory, and other sensory stimuli and transmit them to the brain; sensory information that has registered in the brain but has not been interpreted

Perception The process by which sensory information is actively

organized and interpreted by the brain

Sensation….imp. concepts Stimulus: A source of physical energy that produces

a response in a sense organ. Sensation: A process by which an organism

responds to a stimulus. Intensity: The strength of a stimulus. Psychophysics: The study of the relationship

between the physical nature of stimuli and a person’s sensory responses to them.

Cont. We do not detect all of the stimuli that are present.

Senses are limited or restricted.

Absolute Threshold: The smallest amount of physical intensity by which a stimulus can be detected.

Noise: Background stimulation that interferes with the perception of other stimuli.

The Five SensesHumans are credited with

five basic senses: Seeing Hearing Smelling Tasting Touching

Vision Stimulus for Vision-----Light waves

(Electromagnetic waves to which our eyes are sensitive & capable of responding.

Electromagnetic waves are measured in wavelengths.

Every wave length refers to different level of energy. Range of wave lengths to which humans are

sensitive →Visual Spectrum

Visual System Human visual system consist of the Eyes,

several parts of the brain, and the pathways connecting them.

The Eye : consist of two systems1. Image forming system2. Image transduction System

Eye Image forming System: consist of following

structures:1. Cornea .…front surface of eye: light enters here.

Its a transparent protective window into eyeball, constantly being washed by tears, keeping it moist and clean.

2. Pupil …. A circular opening which changes size in response to the incoming amount of light.

Size of pupil opening depends on the amount of light in the surroundings

Vision

Eye 3. Iris ….The colored part of the eye, ranges from light

blue to dark brown.4. Sclera…. The sclera is commonly known as "the

white of the eye."  It is the tough, opaque tissue that serves as the eye's protective outer coat.

5. Lens …. Located behind the pupil, focuses the light by changing its own thickness, through a process called Accommodation.

Accommodation: The ability of the lens to vary its shape in order to focus incoming images on the retina.

Eye Kind of accommodation depends on the location of

the object distant objects → relatively flat lens Close objects → Thick, rounder lensHaving traveled through pupil and lens ,light waves

reach its ultimate destination in the eye.6. Retina : Part of the eye that converts the electro

magnetic energy of into useful information for the brain.

It is actually a thin layer of nerve cells at the back of the eye ball.

Cont. Two types of light sensitive

receptor cells in Retina Rods → long &

cylindrical ( perform well poor light, insensitive to color & small details, used for peripheral vision & night vision)

Cones → short, thick, cone shaped (responsible for sharp focus and color perception, particularly in bright light)

Peripheral Vision: The ability to see objects outside the eye’s main center of focus.

Eye7. Fovea : part of retina, where concentration of

cones are greatest. Best at seeing details. It helps in focusing on something of particular

interest. No rods in Fovea.

Cont. Optic Nerve: Nerve at the back of the eyeball

that carries neural impulses (visual information) from the eye to the brain.

Cont. Blind Spot: point at which

the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there

Optic Chiasm: A point between and behind the eyes at which nerve impulses from the optic nerves are reversed and “righted” in the brain.