Week 5 - colour perception

• people see different colours in the dress due to overexposure leading to the measured colours being different from the colours measured on the real dress
• overexposure is not the only cause due to people varied in how they saw the colours in the photo not just between the photo and the real dress
• viewing conditions can effect colour perception such as image size and angle
• viewing conditions not only factor due to under lab conditions there is still a difference in colours
• people apply different names to the same colours meaning the forced choice may have effected the difference
• the visible spectrum is the spectrum that human eyes are sensitive to
• humans have 3 cone types
• each photoreceptor responds to a wide range of colours but most strongly to one particular colour
• we have one type of rod receptor for night vision so we are all colour blind at night
• colour blind is most common when you have a mistuned green cone so cant discriminate between certain colours well
• people with no cones are called rod monochromats
• cone monochromat means only one cone type
• cerebral achromatopsia is a cortical colour blindness where following a stroke patients cant see colour at all
• colour blindness does not explain the dress illusion due to their being imbalance between the amount of people who are colour blind (low) and differing answers (high)
• colour centre surround cells in the retina normally transit only the colour edges. The cortex must then reconstruct the body colour of the object. Therefore the stripes in the dress could facilitate filling in and alrtering perception
• simultaneous colour contrast is when the perception of a colour is offset by surrounding colours
• colour after effect is when focus on one colour or image leads to an illusion afterwards
• V8 seems responsible for the conscious perception of colour
• V1 does not discount ambient light whereas V4 does
• individual differences in the yellow blue system may promote one perception over another
• cerebral achromatopsia results from a loss of area V8
• colour constancy is our ability to ignore the colour of the light source which happenes in areas V4 or 8
• simple cells are orientation, position, size selective. Have separate on/ off regions
• simple cells in V1 respond to edges at particular locations and orientations within the visual field
• complex cells maintain orientation sensitivity, spatial frequency sensitivity, and have high resting output. Not sensitive to line position within receptive field
• complex cells are orientation, size and position selective with length summation and no separate on/ off regions
• hyper complex cells are sensitive to line length and orientation and cell is turned off by stimulus outside its classical receptive field. They have a peak for sensitivity and line orientation
• texture is important to differentiate thing such as road and pavement
• texture is spatial detail at a scale finer than which the observer currently defines as the object scale - defined by statistical properties rather than absolute values
• if 2 textures have the same statistical properties they are the same
• a texton (texture atom) is the simplest defining properties of texture (based on properties of V1 cells)
• Broken Ls and Ts are hard to differentiate due to both having 6 textons
• texture segmentation based on line crossings and endings is more ffected by certain visual manipulations then is segmentation by orientation
• the tilt after effect is an example of inhibition over time in the V1 area
• perceived orientation is not determined by activity of one cell, but rather by a population of cells sensitive to different orientations: the neural code
• the response of active cells is changed by adaptation or inhibition over time
• Cells in area V1 that respond to different orientations.
• Simple cells are sensitive to orientation and position.
• Complex cells are sensitive to orientation only.
• Hyper-complex cells are sensitive to orientation and length.