CHAPTER 14 Flashcards
(29 cards)
Table 14.1
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Absolute threshold
The absolute threshold is the minimum amount of stimulus energy needed for an observer to perceive a stimulus, in ideal conditions, 50 per cent of the time.
3 stages of sensation
Reception
Transduction
Transmission
Reception
the stimulus energy is collected by the sense organ.
Transduction
The stimulus energy is converted by the receptor cells into electrochemical nerve impulses.
Transmission
The receptor cells send the nerve impulses to the primary sensory cortex
where specialised receptor cells respond as the process of perception begins.
3 stages of perception
Selection
Organisation
Interpretation
Selection
We can’t possibly pay attention to all the millions of stimuli that we receive at the same time, so we pick out the ones that are important to us and pay attention to those.
Organisation
UWhen the information reaches the brain, it is reorganised so that we can make sense of it.
Interpretation
Past experiences, motives, values and context (including stimulation) are involved in the process where the stimulus is given meaning.
The actual image on our retina is:
> upside-down
back-to-front
blurred
crisscrossed by a network of veins
patched by holes.
Reception in vision
Light enters the eye through the cornea, a tough transparent tissue covering the front of the eye. It then passes through the pupil – the hole in the middle of the coloured part of the eye (the iris). The lens focuses the light on the retina, which contains the photoreceptors – light-sensitive cells called rods and cones.
Transduction in vision
The electromagnetic energy that we know as light energy is converted by the rods and cones into electrochemical nerve impulses. This allows the visual information to travel along the bres of the optic nerve to the brain.
Transmission in vision
The next task for the rods and cones is to send the nerve impulses along the optic nerve to the primary visual cortex in the occipital lobes, at the very back of the brain where specialised receptor cells respond as the process of visual perception continues.
Figure 14.3
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Selection in vision, feature detectors
Millons of stimuli enter the eye and it is impossible to process them all
at once, so we are selective about what we give our attention. At this stage of the process, the image is broken up by specialised cells called feature detectors. Feature detectors are cells that individually respond to lines of a certain length, lines at a certain angle or lines moving in a certain direction. Feature detector cells are found in the optic nerve and in the primary visual cortex.
Organisation in vision
Our visual cortex in the brain recorganises information so that we can make sense of it. We do this by using certain visual perceptual principles (see Chapter 15):
> perceptual constancies
> Gestalt principles
> depth cues.
Once the image is re-assembled using these principles, it travels along two pathways simultaneously: to the temporal lobe, to identify the object, and to the parietal lobe, to judge where the object is in space (in relation to our visual eld and ourselves).
Interpretation in vision
This is the process whereby the visual stimulus/object is given meaning. The temporal lobes identify what the object is by comparing incoming information with information already stored in the memory.
Reception and light energy
The process of light entering the eye is an important part of our ability to receive and interpret a visual stimulus.
The light energy must be within the visible part of the electromagnetic spectrum. Wavelengths of between 360 and 760 nanometres form the visible spectrum (1 nm = 1 billionth of a metre). The energy that enables us to see is what we call light energy, the visible part of the electromagnetic spectrum.
Retina and the two photoreceptors
The retina is nerve tissue that covers more than 50 per cent of the inner surface of the back of the eye. It contains two types of photoreceptors: rods and cones.
Rods
Rods: There are 125000000 in each eye.
- They are responsible for vision in low light (that is, they are very sensitive to light).
- They are responsible for peripheral vision (out of the corner of the eye).
- They are concentrated at the edges of the retina.
- They have low visual acuity (they can’t register detail).
- They can register only in black and white.
- They are most sensitive to light of approximately 500 nm wavelength.
Cones
There are 6500000 in each eye.
- They are concentrated in the middle of the retina.
- They are responsible for vision of detail.
- They are responsible for colour vision (and black-and-white vision in daylight).
- They require high levels of light to enable them to respond.
Taste buds, organ of taste, taste
The organ of taste is, of course, the tongue, on which are located most of the 10000 taste buds that are located in our mouth and throat. Each taste bud contains between 50 and 150 taste receptor cells. Each taste-cell lives only about 10 days – new cells grow at the edge of the taste bud and move inwards towards the centre and then die.
5 tastes
Bitter Sweet Salty Umami sour
