Week 8 Flashcards
Process of how light enters the eye
Light enters the cornea
The light passes through the pupil
The lens focuses the light on the retina
Cornea
a clear covering that protects the eye and begins to focus the incoming light
pupil
a small opening in the centre of the eye
iris
The coloured part of the eye and controls the size of the pupil by constricting or dilating in response to light intensity
lens
A structure that focuses the incoming light on the retina
retina
the layer of tissue at the back of the eye that contains photoreceptor cells
Visual accommodation
the process of changing the curvature of the lens to keep the light entering the eye focuses on the retina.
Rays from the top of the image strike the bottom of the retina, rays from the left side of the image strike the right side of the retina, causing the image on the retina to be upside down and backward
Nearsighted
If the focus is in front of the retina
Farsighted
When the focus is behind the retina
Activation of rods and cones
The activation then spreads to the bipolar cells and then to the ganglion cells, which gather together and converge, like the strands of a rope, forming the optic nerve
optic nerve
a collection of millions of ganglion neurons that sends vast amounts of visual information, via the thalamus, to the brain
electromagnetic energy
pulses of energy waves that can carry information from place to place
Wavelength
the distance between one wave peak and the next wave peak.
Visbile spectrum
the part of the electromagnetic spectrum that our eyes detect (only the range from about 400 to 700 billionths of a meter)
Rods
Visual neurons that specialize in detecting black, white, and gray colours. There are about 120 million in each eye. They do not provide a lot of detail about the images we see, but because they are highly sensitive to shorter waved and weak light, they can help us see in dim light. Located primarily around the edges of the retina, so they are particularly active in peripheral vision.
Cones
Visual neurons that are specialized in detecting fine detail and colours. The five million in each eye allow us to see colour, but they operate best in bright light. Located in and around the fovea
Fovea
Central point of the retina
How sensory information is recieved
sensory information is received by the retina and then relayed through the thalamus to corresponding areas in the visual cortex, which is located in the occipital lobe at the back of the brain
Left and right eyes send information to both the left and right hemisphere, and the visual cortex processes each of the cues separately and in parallel
visual cortex turns the sensations they receive from the optic nerve into meaningful images
why do we have a blind spot
There are no photoreceptor cells at the place where the optic nerve leaves the retina, so a hole or blind spot in our vision is created
How is perception created
In a part through the simulataneous action of thousands of feature detector neurons, located in the visual cortex, that respond to strength, angles, and movements of a visual stimulus
Feature detectors work in parallel, each performing a specialized function. Activation is passed onto other parts of the visual cortex, where other neurons compare the information supplied by the feature detectors with images stored in memory
Many neurons fire together, creating the single image of the red square that we experience
Helmoltz trichromatic colour theory
what colour we see depends on the mix of the signals from the three types of cones: one that reacts primarily to blue light, one that reacts to green-light, and one that reacts to red light. If the brain receives messages from all three types of cones, it will perceive white
Opponent process theory
proposes that we analyze sensory information not in terms of three colours, but rather in three sets of “opponent colours”: red-green, yellow-blue, and white-black
Evidence comes from the fact that some neurons in the retina and in the visual cortex are excited by one colour
How do the tricolour and opponent process mechanisms work together to produce colour vision
When light rays enter the eye, the red, blue, and green cones on the retina respond in different degrees and send different strength signals of red, blue, and green through the optic nerve
colour signals are then processed by both the ganglion cells and by the neurons in the visual cortex
feature detector neurons
Specialized neurons, located in the visual cortex, that respond to the strength, angles, shapes edges, and movements of a visual stimulus
colour blindness
The inability to detect green and/or red colours
Gestalt
A meaningfully organized whole
Perceiving form
figure and ground, similarity, proximity, closure
figure and ground
we structure input so that we always see a figure (image) against a ground (background)
Similarity
stimuli that are similar to each other tend to be grouped together
proximity
we tend to group nearby figures together
Continuity
we tend to perceive stimuli in smooth, continuous ways rather than in more discontinuous ways
Closure
We tend to fill in gaps in an incomplete image to create a complete whole object
Depth perception
the ability to perceive three-dimensional space and to accurately judge distance. Without it, we would be unable to drive a car, thread a needle, or simply navigate our way around
Visual cliff
A mechanism that gives the perception of a dangerous drop-off, in which infants can be safely tested for their perception of depth
Binocular depth perception
depth cues that are created by retinal image disparity- the space between our eyes - and which thus require the coordination of both eyes
Depth cues
Messages from our bodies and the external environment that supply us with information about space and distance
Convergence
the inward turning of our eyes that is required to focus on objects that are less than about 500 feet away from us
How the visual system uses accomodation to help determine depth
As the lens changes its curvature to focus on distant or close objects, information relayed from the muscles attached to the lens helped us determine an object’s distance. Only effective at short viewing distances
Monocular depth cues
Depth cues that help us perceive depth using only one eye
Position
We tend to see objects higher up in our field of vision as farther away
Relative size
Assuming that the objects in a scene are the same size, smaller objects are perceived as farther away
Linear perspective
Parallel lines appear to converge at a distance
Light and shadow
The eye receives more reflected light from objects that are closer to us. Normally, light comes from above, so darker images are in shadow
Interposition
When one object overlaps another object, we view it as closer
Aerial perspective
objects that appear hazy, or that are covered with smog or dust, appear farther away
Beta effect
refers to the perception of motion that occurs when different images are presented next to each other in succession. The visual cortex fills in the missing part of the motion, and we see the object moving. Used in movies to create the experience of motion
Phi phenomenon
We perceive a sensation of motion caused by the appearance and disappearance of objects that are near each other. Looks like a moving zone or cloud of background colour surrounding the flashing objects
Sensory modalities
A type of sense; for example, vision or audition
unimodal stimuli
Of or pertaining to a single sensory modality
multimodal
Of or pertaining to multiple sensory modalities
multimodal perception
The effects that concurrent stimulation in more than one sensory modality has on the perception of events and objects in the world
Integrated
The process by which the perceptual system combines information arising from more than one modality
superadditive effect of multisensory integration/ multisensory enhancement
The finding that responses to multimodal stimuli are typically greater than the sum of the independent responses to each unimodal component if it were presented on its own
unimodal components
the parts of a stimulus relevant to one sensory modality at a time
Principle of inverse effectiveness
the finding that, in general, for a multimodal stimulus, if the response to each unimodal component is weak, then the opportunity for multisensory enhancement is very large. However, if one component-by itself-is sufficient to evoke a strong response, then the effect on the response gained by simultaneously. Processing the other components of the stimulus will be relatively small
superior temporal sulcus
Contains single neurons that respond to both the visual and auditory components of speech
multisensory convergence zones
Regions in the brain that receive input from multiple unimodal areas processing different sensory modalities
Superior colliculus
Receives inputs from many different areas of the brain, including regions involved in the unimodal processing of visual and auditory stimuli. Involved in the “orientating response”
orientating response
the behaviour associated wtih moving one’s eye gaze toward the location of a seen or heard stimulus
Receptive field
The portion of the world to which a neuron will respond if an appropriate stimulus is present there
If a stimulus is presented in a neuron’s receptive field
That neuron responds by increasing or decreasing its firing rate
If a stimulus is presented outside a neuron’s receptive field
Then there is no effect on the neuron’s firing rate
Neural convergence
When two neurons send their information to a third neuron, the third neuron’s receptive field is the combination of the receptive fields of the two input neurons
Crossmodal receptive fields
A receptive field that can be stimulated by a stimulus from more than one sensory modality
Crossmodal stimuli
A stimulus with components in multiple modalities that interact with each other
How does the overlap of the crossmodal receptive fields play a vital role in the integration of crossmodal stimuli
When the information from the separate modalities is coming from within these overlapping receptive fields, then it is treated as having come from the same location and the neuron responds with a superadditive response
Part of the information that is used by the brain to combine multimodal inputs is the location in space from which the stimuli came
Spatial principle of multisensory integration
Multisensory enhancement is observed when the sources of stimulation are spatially related to one another
Unimodal cortex
a region of the brain devoted to the processing of information from a single sensory modality
Primary visual cortex
Area of the cortex involved in processing visual stimuli
Primary auditory cortex
Area of the cortex involved in processing auditory stimuli
What is the first stop in the cortex for information arriving from the eyes
primary visual cortex
Two ways for multimodal interactions to occur
- The processing of auditory information in relatively late stages of processing feeds back to influence low level processing of visual information in unimodal cortex
- Areas of the unimodal cortex contact each other directly, such that multimodal integration is a fundamental component of all sensory processing
multimodal phenomena
Concerns the binding of inputs from multiple sensory modalities and the effects of this binding on perception
Crossmodal phenomena
Concerns the influence of one sensory modality on the perception of another
Rubber hand illusion
The false perception of a fake hand as belonging to a perceiver, due to multimodal sensory information
double flash illusion
The false perception of two visual flashes when a single flash is accompanied by two auditory beeps
Crossmodal speech effects
Usually show altered perceptual processing of unimodal stimuli by virtue off prior experience with the alternate unimodal stimulus
perception of collisions between two circles
The tendency to perceive two circles as bouncing off each other if the moment of their contact is accompanied by an auditory stimulus
Crossmodal finding
Familiarity with this visual information has led to increased recognition of the speaker’s auditory speech, to which participants had never had exposure
When perceives see a speaking face
The visual form of a speaker engaged in the act of speaking appears to contain information about what that speaker should sound like. The auditory form of speech seems to contain information about what the speaker should look like
Accuracy of identifying the spoken words was much___
Higher for the audiovisual condition than it was in the auditory alone condition
