extra reading PAA

Snowden (2002) visual attention to colour

experiments looking at abrupt changes in colour have failed to find similar attentional capture - consistent with current theories of the role of magnocellular and parvocellular streams that postulate that the M stream - which is colour blind - plays the dominant role in guiding attention and eye movements

in this study, colourful stimuli were as effective as those containing large luminance signals in guiding attention

used Posner’s cueing paradigm

isolated the P stream - suggests that this stream is also capable of attentional capture

colour vision not only aids target identification but also is a strong aid for target detection and localisation

what do experiments using colour-blind people show us?

the disabilities experienced by colour-blind people show us the biological advantages of colour vision in detecting targets, in segregating the visual field and in identifying particular objects or states

human dichromats have especial difficulty in detecting coloured fruit against dappled foliage that varies randomly in luminosity

the two colour systems and their functions

primordial system = exists almost exclusively for colour vision

the second subsystem = at the early stages of the visual pathway, this chromatic information is carried by a channel that is also sensitive to spatial contrast

LM (motion blindness)

one major role of extrastriate cortical processing might be the interpretation of stimuli that suffer from an impaired signal-to-noise ratio

Braddick

when a group of dots within a random-dot array is discontinuously displaced, it appears as a moving region perceptually segregated from its stationary surround (low-level) - different spatial and temporal constraints from classic apparent motion of isolated stimulus elements (high-level)

Newsome et al - spatiotemporal range of directional interactions in MT and V1

the spatiotemporal limits for perception are similar to the limits for direction selectivity in MT neurons, but differ markedly from those for V1 neurons

suggests a correspondence between neuronal responses in MT and the short-range process of apparent motion

Zeki et al

PET scans using Enigma illusory motion vs no illusory motion

when participants perceived illusory motion, the increases in rCBF took place in regions closely related to V5, there was also activity in other cortical areas outside the visual cortex, not present when the subjects had been viewing objective motion

Corbetta and Shulman (2002) neural basis of attention (extra info)

humans use cognitive information to direct attention to relevant objects in a visual scene

an attentional set aids detection of and response to targets

the dorsal frontoparietal system seems to maintain a salience map that combines bottom-up with top-down information during visual search

suggest that neglect results from damage to the ventral network that also functionally inactivates the dorsal network