PSYU2239 Perception - Vision Flashcards
What is spatial vision?
The term spatial vision encompasses all things related to seeing the space around us. This definition is so broad that it includes everything related to vision; however, it is usually restricted to visual perception of non-moving two-dimensional luminance patterns.
What is light?
A wave of electromagnetic radiation.
What is the visible spectrum for the human eye?
The visual electromagnetic spectrum is 400-700 nm
What are illusions?
An instance of a wrong or misinterpreted perception of a sensory experience.
What are aftereffects?
The perception that a stationary object or scene moves following prolonged fixation of a moving stimulus. The illusory movement is in the opposite direction to the movement of the stimulus that induced the effect. The best known example is the waterfall illusion, produced by watching a waterfall for a period and then shifting one’s gaze to the stationary surrounding scenery; the stationary objects appear to move upward.
Name the discussed illusions with explanations.
Illusions
Bistable figures and illusory contours - these demonstrate that perception is much more than just a simple automatic process what you see is what’s there. Active process. Vision is a bottom up process but these illusions remind us that there are top-down influences happening as well. Higher processes can influence what is perceived, despite no change in sensory input. Although vision is unidirectional, receptor to cortex, there are lateral and backward connections forming feedback loops, sensory information can travel in all directions.
Size illusions
The brain processes size of object and depth a particular way. Perceptual systems have developed a process called constancy scaling which compensates for these distance related changes in image size. Example, an image on the retina shrinks is more likely to be perceived as maintaining its size as it recedes into the distance.
Muller-Lyer illusions
Railway tracks - the two railway lines between the vertical tracks. The top line is perceived as larger as we apply the constancy scaling rule to it and assume we are looking at a 3D object not a 2D object.
Ponzo illusions
Define bottom-up stimulus and top-down influences.
Bottom-up processing in psychology is the sensory perception of the outside stimuli, the stimuli being processed in the part of the brain responsible for that sense, and then deriving meaning from analysis based only on data.
Top-down processing refers to how our brains make use of information that has already been brought into the brain by one or more of the sensory systems. Top-down processing is a cognitive process that initiates with our thoughts, which flow down to lower-level functions, such as the senses.
Define luminance.
- the intensity of light emitted from a surface per unit area in a given direction. 2. a measure of the brightness of a luminous surface, measured in candelas per unit area.
Define on-centre off-centre.
The receptive fields of retinal ganglion cells and thalamic neurons are organized as two concentric circles with different contrast polarities.
ON-centre cells are depolarized by illumination of their receptive field centre (RFC), while Off-centre cells are depolarized by decreased illumination of their RFC.
Define optic chiasm.
The optic chiasm contributes in conveying visual information from the eye to the cortex. It receives visual information from the optic nerve and transmits this information to the optic tracts.
The optic chiasm, or optic chiasma, is the part of the brain where the optic nerves cross and is therefore of primary importance to the visual pathway.
Explain the right and left visual fields.
Visual processing in our brain helps us understand what we see. The right side of our brain controls the left visual field, and the left side controls the right visual field. This happens through the optic chiasm, where information from our eyes converges before being sent to the brain.
What is the LGN?
The LGN is the lateral geniculate nucleus (LGN) belongs to the category of sensory projection nuclei of the thalamus and plays an essential role in normal visual processing.
Like ganglion cell properties in that they have centre-surround antagonism
Retinotopically organised
Are monocular both eyes have inputs to LGN, but each eye goes to separate layers
Only one visual hemifield (contra or opposite side)
Transmits visual information to the visual cortex.
What is the difference between the V1 and LGN?
V1 is “primary” because the LGN sends most of its axons there, so V1 is the “first” visual processing area in the cortex. V1 processes the information coming from the LGN (as described below) and then passes its output to the other visual cortical areas which are (creatively) named V2, V3, V4, etc.
What are the properties of the LGN
The LGN consists of six eye-specific layers, four of which receive inputs from parvocellular retinal ganglion cells, and two of which receive magnocellular inputs.
Also new class of cells called the koniocellular cells, might be blue yellow processing
What is a focal lesion?
Brain lesions are areas of brain tissue that show damage from injury, disease, or poisoning (drugs alcohol CO2). Reasonably well located to a single sit or small number of sites.
