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Perception
Perception refers to the process by which we give meaning to sensory information, resulting in our personal interpretation of that information.
Stimuli
External energy in the environment that elicits or influences a physiological or psychological response.
Air vibrations for hearing (garage band)
Sound waves youtube
Chemical Stimuli for smell
What do you think is our most important sense?
STEP 1: Physical Energy in the Environment
• Sensory receptors in each sensory system detect physical energy from the external environment.
ElectromagneticEnergy
MechanicalEnergy
ChemicalEnergy
Selective attention
Ability to focus on stimuli in our environment while ignoring less relevant information.
Selective attention video
How do we hear someone in a busy room.
Light enters the eye through the cornea, the aqueous humor and then
the lens.
All of these have a part to play in focusing but the lens plays the
greatest role.
Light
Lens
In order to focus light onto the retina, the lens adjusts its shape according to the distance of the object being viewed. Its shape is changed by the ciliary muscles attached to each end of the lens.
These muscles expand and contract, the lens to automatically bulge to focus nearby objects onto the retina and flatten to focus distant objects onto the retina.
The iris is a ring of circular muscles that contracts or expands to change the
size of the pupil, regulating the amount of light that enters the eye.
The cornea
a transparent, convex shaped (curved outwards) covering which protects the eye and helps to focus light rays onto the retina at the back of the eye.
Projection of an image to the retina
The lens of the eye is convex, or curved, in shape.
Light rays do not bend.
As light rays travel in a straight line through the lens, the image projected on the retina is inverted and reversed.
Photoreceptors
The sensory receptors for vision are located in the retina of the eye and are called photoreceptors.
Photoreceptors are specialised neurons that detect electromagnetic energy and convert it into electrochemical energy (or neural impulses), a format the brain can receive and process
Blue man group video (Activity 3.5 and 6 p85)Rods Cones
Activity 3.8 pg 86
The difference between Rods and Cones
Rods ConesRods are located in the outer regions of the retina.
Peripheral Vision – Rods are distributed in larger numbers in the outer reaches of the retina, which explains why they are used for peripheral vision.
Night Vision – Rods are unable to detect colour. Pure rod vision is black and white. Rods are much more sensitive to light than cones and therefore, allow us to see in very dim light. It takes rods 8 minutes to adapt to the dark.
There are about 125 million rods in each retina.
Cones are located in the central regions of the retina.Colour Vision – Cones produce colour sensations.Daylight Vision – Cones work best in bright light. They do not operate well in dim light, which explains why colour becomes difficult to identify in low light or in darkness. (It takes cones about 30 minutes to adapt to dark conditions.)Visual Acuity – Cones detect fine detail.
There are about 6.5 million cones in each retina.
Visual Acuity: Fovea
The fovea is a tiny cup-shaped area located in the centre of the retina. The fovea is only 0.3mm in diameter and contains only cones (about 50,000).
Cones are very densely concentrated in the fovea, and so the sharpest images are those focused on this small area.
If you look at your thumbnail at arm’s length, its image just about covers the fovea.
Visual acuity steadily decreases towards the edge of the retina.
Absolute threshold
The lowest level of stimulus that is required to detect that the stimulus exists.
Quietest sound
Weakest light
Lightest touch
Determined by measuring the minimum amount of stimulus that can be detected 50% of the time
Differential threshold
Smallest noticeable difference in a change in levels of a stimulus
Turning up a stereo
Weight difference