Watanabe Experiment
Researchers separately examined the effects of top-down attention and visual awareness on the BOLD signal in the human V1
Two-by-two factorial design:
- visibility of the target stimulus (visible or invisible)
- directed attention (target or nontarget location)
Watanabe Experiment: Findings
When multiple patches of smaller motion gratings (Dynamic Mondrians) were shown to the opposite eye as that of the perceptual target, the target was rendered invisible because of binocular suppression
–> when they were shown to the eye of the perceptual target, the target remained visibile
Attention vs. Awareness (Watanabe)
- attention but not awareness modulates the BOLD signal in the human V1 during binocular suppression
- the BOLD response was unaffected by whether the participant lying in a scanner saw the target or not
- visual awareness and visual attention are two dissociated functions in the visual system
- supported by distinct neuronal mechanisms
Attention and Consciousness
- attention and consciousness are related yet different
- one can attend to an object without becoming aware (conscious) of it
Hypothesis by Crick and Koch
V1 neurons do not directly contribute to visual awareness
- it may be that consciousness (awareness) does modulate neuronal response in V1 during continuous binocular rivalry (suppression) but not at the onset of rivalry induced by a short-duration stimulus
Lamme: Why visual attention and awareness are different
Selectiveness –> we are not aware of everything we lay our eyes on
Neuroscience –> there is neural activity that produces conscious experience and neural activity that does not
–> we are aware of what is in the focus of attention
Awareness and Attentive Selection
- change blindness and inattentional blindness hint at selective processes
- even though we think we see everything that is in front of us, we actually have a very limited conscious representation of the outside world
–> many sensory inputs reach the brain and, via the process of attentive selection, some of these reach a conscious state, which allows us to report about them
Classes/Levels of Selection
Unconscious, unattended, and attended
Option 1: only attended stimuli reach awareness
Option 2: there is no difference between attended and conscious stimuli
Separating Awareness from Attention
Attention does not determine whether stimuli reach a conscious state but determines whether a conscious report about stimuli is possible
–> attention determines whether items are stored in a sufficiently stable manner (working memory)
–> we are conscious of many inputs but, without attention, this conscious experience cannot be reported and is quickly erased and forgotten
External (Exogenous) Attention
- salient stimuli are processed more efficiently than others
- saliency reflect how long-term memory shapes and modifies sensory processing
- something “grabs” your attention
Attentional Priming
- the processing of a stimulus will leave a trace of activated and inhibited neurons that can last for a variable amount of time
–> the processing of subsequent stimuli might benefit from this trace if the two stimuli share properties, resulting in attentional priming
Endogenous Attention
- you direct your attention
- parts of the brain that extract the meaning of the cue, and that are able to relate this to current needs and goals, must preactivate or otherwise facilitate the appropriate sensory pathways
Feedforward Connections
Feedforward connections are capable of generating sophisticated receptive field (RF) tuning properties and thus extracting high-level information, which could lead to categorization and selective behavioral responses
Feedforward Sweep (FFS)
= the earliest activation of cells in successive areas of the cortical hierarchy
- as soon as the FFS has reached an area, recurrent interactions between neurons within that area and neurons that have been activated at earlier lower levels can start
–> visual processing mediated by the FFS is not accompanied by awareness
Backward Masking
Renders a visual stimulus invisible by presenting a second stimulus shortly after the first
–> the masked stimulus, although invisible, still evokes selective feedforward activation in the visual and non-visual areas
–> neurophysiological manifestations of recurrent interactions are suppressed by backward masking
Recurrent Processing (RP)
Conscious visual experience (awareness) requires recurrent processing of interactions between visual and higher areas
Phenomenal Awareness
Perceptual Awareness arises when:
- early visual areas have started to engage in recurrent interactions
- visual features are related to each other, binding and segregation can occur, and perceptual organization evolves
- at low/early levels there is relatively little competition between stimuli, so groups of recurrent interactions representing multiple stimuli are possible
–> unattended process
–> we can have phenomenal awareness of many items in a scene
–> shares neural mechanisms with iconic (sensory) memory
Access Awareness
Access Awareness arises when…
… these recurrent interactions grow more and more widespread and eventually the visual information is put into the context of the systems’ current needs, goals, and full history
–> attended process
–> only a limited number of recurrent groups can span the range from visual to more frontal areas
–> shares neural mechanisms with woking memory
