perceiving and recognizing objects Flashcards
Orientation selectivity
Cells are tuned to detect lines in a specific orientation
Max to vertical contour
Fire less if tilted another way
receptive fields in the striate cortex
cells in the striate cortex respond best to bars of light (edges, lines of specific orientation, motion and size) , rather than to spots of light (which is what the retina and LGN prefer)
interested in the basic features of visual image
the pattern of illumination (or contrast), not the overall light level, is the primary concern of the visual system.
combining info to get more complicated info
Border ownership
when one object is in front of another There will be a visual border formed between the object and the background.
That border is “owned” by the object.
It is the edge of the object, not a property of the background
Extra striate cortex
Region of the cortex bordering the primary visual cortex and containing multiple areas involved in visual processing
Beyond VI
Just lies outside primary visual (striate) cortex
Receptive field properties
Stimulus (bar) length
Orientation
Width (spatial frequency)
Direction of movement
Colour
Ocular dominance
- Cortical neurons respond to both eyes but have a preferred eye (respond more to one eye than the other)
stimulus (bar length)
End stopping
neuron fires less if a bar does
not reach the outside edge of the receptive field or extends beyond the receptive field
Specific to bars of specific length
Contours
sudden transitions in an image
(luminance, colour)
hue can produce contour
the basic elements of visual perception
Without them, we would not see anything (Ganzfeld)
how do you find the edges of objects?
the receptive fields of cells in the primary visual cortex are too small
we are only picking up some - neurons only sensitive to picking up a small area
if we are going by the idea of contours the would have to touch to be the same object (house example of the snowman and car being apart of the house, but the windows are not) - so it is more complicated than this
lack of edge does not bother the visual system
Ganzfeld
People report being blind
Featureless environments
Happens to pilots when they go into a cloud
Snow blindness for skiers
Middle Vision
A loosely defined stage of visual
processing that comes after basic features have been extracted from the image (low-level vision) and before object recognition and scene understanding (high-level vision)
Involves the perception of edges and surfaces
Determines which regions of an image should be grouped together into objects
matching what we perceive with a memory—of something perceived in the past
organize elements of a visual scene into groups we can recognize as objects
Illusory contour
a contour that is perceived even
though nothing changes from one side of the contour to the other
People report seeing something not actually in the image (black is what’s actually seen) but will report seeing arrow
Contour not present, just something we are creating
People try to simply their environment
a line or edge we percieve even though it is not actually there
sometimes our brains fill in gaps to complete an image
Occulusion
notches In the circle seem to be supporting horizontal contour - arrangement of notches may imply that they are a part of a bigger scene
happens when one object obstructs or overlaps an object in the visual scene
our brain uses this so that we can interpret that the overlapping object is in front of the other one
depth cue
Structuralism
a school of thought believing that
complex objects could be
understood by analysis of
the components
Argued that perceptions are the sum of atoms of sensation – bits of colour, orientation, and so forth
Perception is built up of local sensations
Challenged by illusory contours
An extended edge is seen bridging a gap where
no local atom of “edgeness” can be found
Gestalt school
a school of thought stressing that
the perceptual whole could be greater than the apparent sum of the parts
Proximity
items that are near each other tend to group
Because they are closer together
Similarity
similar looking items tend to group
Colour, size, orientation, aspects of form
Conjunctions (combinations) of features do not work well
Texture segmentation
carving an image into regions of common texture properties
No hard contours dividing the regions
Divides images into half.border
Good continuation
a Gestalt grouping rule stating
that there is a tendency to perceive a line as continuing in its established direction
If two contours are close and collinear they are likely to come from the same contour
Closure
a Gestalt principle that holds that a closed contour is preferred to an open contour
The mind tends to fill in gaps in a visual image to perceive it as a whole. This means that if a shape is partially obscured or incomplete, we will still perceive it as a complete object.
Example: If you see a circle that is broken in a few places, your brain will interpret it as a complete circle rather than as separate segments.
Parallelism
parallel contours are likely to belong to the same group
regions with parallel contours are more likely to be seen as figure
Symmetry
symmetrical regions are more likely to be seen as a group
a symmetrical region is more likely to be seen as figure
Common region
items will group if they appear to
be part of the same larger region
Connectedness
items will tend to group if they are
connected
common fate
elements that move in the same direction tend to group together
