Chapter 4 Flashcards
Sensation
- the stimulation of the sense organs
- detection of physical energy by sense organs, which then send information to the brain
Perception
- the selection, organization, identification and interpretation of sensory input, in order to form a mental representation
- the brain’s interpretation of raw sensory inputs
Transduction
- a process in which the sensors in the body convert physical signals from the environment into encoded neural signals sent to the CNS
- a process of converting an external energy or substance into electrical activity within neurons
Sensory adaptation
- a gradual decline in sensitivity due to prolonged stimulation
- a process in which activation is greatest when a stimulus is first detected
Psychophysics
- the study of quantitative relations between psychological events and physical events or, more specifically, between sensations and the stimuli that produce them
Absolute threshold
The lowest level of a stimulus needed to detect a change 50% of the time
Just noticeable difference
Smallest change in intensity of a stimulus that one can detect
Weber’s Law
The change in a stimulus that will be just noticeable is a constant ratio of the original stimulus
Fechner’s Law
Describes the relationship between stimulus magnitude and perceived magnitude. The magnitude of perceived intensity increases proportionally to the logarithm of the stimulus intensity
Steven’s Law
- An empirical relationship between an increased intensity or strength in a physical stimulus and the perceived magnitude increase in the sensation created by the stimulus
- Basically, it’s an equation/law that expresses the fact that our perception of how much the stimulus has increased is not the same as how much the stimulus has actually increased
- After a certain point, increasing the strength of the electric shock by just a little bit makes us perceive a much stronger electric shock– we think that the magnitude of the shock has increased by a lot more than it really has!
- After a certain point, we need to increase brightness by a lot to perceive a difference in the magnitude of brightness (opposite trend from the electric shock)
Bottom up processing
Begins with perception of raw stimuli and ends with our synthesizing them into a meaningful concept
Top down processing
Begins with beliefs and expectations which are imposed onto raw stimuli
Iris
Coloured ring of muscle surrounding the pupil, which helps regulate the amount of light passing into the eye
Pupil
Hole through which light passes; size controlled by the iris
Sclera
The white part of the eyeball
Cornea
Curved, transparent layer covering the iris and pupil; bends incoming light to focus the incoming visual image at the back of the eye
Lens
Part of the eye that changes curvature to keep images in focus; changes shape to allow us to see both distant objects and nearby objects
Retina
- Thin membrane at the back of the eye; contains two types of photoreceptor cells (rods/cones)
- Also consists of bipolar neurons and ganglion cells
- The photoreceptors convert light stimuli into electrical nerve impulses
- The nerve impulses are transmitted via bipolar neurons to ganglion cells
- The ganglion cells are apart of the optic nerve fibre, which then sends the electrical nerve impulses to the brain
Fovea
Central part of the retina; responsible for acuity; only contains cones
Acuity = sharpness of vision
Rods
One of two receptor cells found in the retina Much more plentiful than cones Long and narrow Allow us to see basic shapes/forms Good for nighttime and peripheral vision Monochromatic
Cones
One of two receptors cells found in the retina
Less abundant than rods
Shaped like cones
Good for daylight vision and colour vision
Three types, blue/green/red, that are sensitive to different wavelengths of light
Optic nerve
Transmits impulses from the retina to the rest of the brain
Optic disk/Blind spot
A hole in the retina where the optic nerve exits the eye; region of the retina containing no rods and completely devoid of sense receptors; the place where the optic nerve connects to the retina
Optic chiasm
Point at which the optic nerves from the inside half of each eye cross over and project to the opposite half of the brain
Ciliary body
Controls the shape of the lens
Eye muscle
Controls movement of the eye
Accomodation
changing the shape of the lens to focus on objects near or far; flat lens (long/skinny) allow us to see distant objects; fat lens (short/wide) allow us to see nearby objects
Pathway of light
Cornea Pupil Lens Retina (rods/cones → bipolar neuron → ganglion cell → optic nerve) Optic nerve Optic chiasm Visual cortex
Receptive Fields
A collection of rods and cones that funnel signals to a particular visual cell in the retina
When stimulated, this field affects the firing of the visual cell
There are two types of receptive fields: center-on (excitatory center) and center-off (inhibitory center)
Feature detectors
- neurons that respond selectively to very specific features of more complex stimuli
- two types: simple cells and complex cells
- Feature detector cells detect lines and edges
- Hubel and Wiesal found that some cells in the visual cortex fire in response to slits of a specific orientation/location (simple cells) while other cells fire in response to movement of slits in a specific direction/orientation (complex cells)
Simple cells
respond best to lines of correct width, orientation and location in receptive field
Complex cells
respond best to movement of lines in a specific direction
Trichromatic theory
Idea that colour vision is based on our sensitivity to three primary colours: blue, green and red
We have three types of cones that have different sensitivities to certain frequencies of light
Colours other than blue/green/red are a result of the additive mixing of light (combinations of blue/green/red)
Opponent process theory
Colour perception depends on receptors that make antagonistic responses to three pairs of colours: blue/yellow, green/red, and white/black
The presence of green inhibits red and vice-versa in that particular spot on the visual field; same with blue/yellow and white/black