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. Electromagnetic Energy Mechanical Energy Chemical Energy
Stimuli Light stimuli for sightActivity 3.4 p81
Selective attentionSelective 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.
The eyeThe eye
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 shape of the lens can determine near and short sightedness
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 corneaThe cornea a transparent, convexshaped (curved outwards) covering which protects the eye and helps to focus light rays onto the retina at the back of the eye.
Electromagnetic energy, or visible light, is received on the retina of the eye.
Projection of an image on the retina
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.
Structure of the RetinaStructure of the Retina
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) RodsCones Activity 3.8 pg 86
The difference between Rods and Cones RodsCones Rods 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: FoveaVisual 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 thresholdAbsolute 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 thresholdDifferential threshold Smallest noticeable difference in a change in levels of a stimulus Turning up a stereo Weight difference
Visual perception processVisual perception process