CogNeuro 6-7 Flashcards
Endogenous versus Exogenous
Endogenous: voluntary, top-down attention. controlled by internal factors such as goals, expectations, and cognitive strategies. Ex: focusing on reading a book
Exogenous attention: reflexive, bottom-up attention. captured automatically by external stimuli in the environment. Ex: shifting attention to a flashing light
What are the 4 hypotheses as to what effect attention has on neural activity
tuning gain, tuning width, tuning shift, orientation selectivity
Tuning Gain Hypothesis
suggests that attention increases the amplitude of gain of neural responses to the attended stimuli. In other words, neurons become more responsive to preferred stimuli when attention is directed to them. (basically gain change)
Tuning Width Hypothesis
suggests that attention can affect the selectivity of neurons by narrowing or sharpening their tuning curves. This means that neurons become more selective for specific features, reducing their response to non-preferred stimuli.
Tuning Shift Hypothesis
suggests that attention can cause a shift in the tuning curve of neurons toward the attended stimuli. Neurons become more responsive to the features or stimuli that are the focus of attention.(no change in tuning asymptote, vertical shift)
Orientation Selectivity Hypothesis
relates to visual processing and proposes that attention can enhance the selectivity of neurons for specific orientations. Neurons become more tuned to the orientation of stimuli that are attended. (no change in orientation selectivity (horizontal shift))
What is gain change? And what areas are subject to gain change?
Gain change (multiplier to the gaussian tuning function) refers to a multiplicative effect and emphasizes that attentional modulation acts as a multiplier on neural responses. This is a more flexible and dynamic way of shaping neural activity compared to a simple additive shift.
V4 (stimulus orientation) and MT (middle temporal)/MST (medial superior temporal) neurons (motion direction) are subject to a “multiplication” of activity as a function of attention.
Task and Results of “attention in V4” study/
Animals were trained to perform a delayed match-to-sample task in which oriented stimuli were presented in the receptive field of the neuron being recorded. On some trials the animals were instructed to pay attention to those stimuli, and on other trials they were instructed to pay attention to other stimuli outside the receptive field. In this way, orientation-tuning curves could be constructed from neuronal responses collected in two behavioral states: one in which those stimuli were attended by the animal and one in which those stimuli were ignored by the animal.
Checking the normalized response of the neuron, we see a clear amplitude difference between attended and unattended stimuli. Neurons in the unattended condition exhibited lower amplitude and gain compared to the attended counterparts. This suggests that attention acts as a multiplier to the Guassian tuning function that measures neuronal activity. In layman terms, attention seems to make the neuron activate more for the same piece of stimulus.
Concludes tuning gain hypothesis.
Task and Results of “attention in MT/MST” study – testing motion detection
An experiment was conducted where the animals needed to pull a lever when an observed object changed speed, and then researchers checked the signals in the MT/MST, with the independent variable specifically being whether or not the stimulus was being attended (orientation and other variables were controlled for).
Results: The results were pretty conclusive in showing that attention was an important factor for motion detection. There were two ways this was shown: (1) When you didn’t pay attention to things in the receptor field and looked outside instead, the spiking activity was meaningfully lower (2) When they did this while checking selectivity within the RF itself, they showed that the motion stimulus is strongly gated by attention (without attention, motion isn’t really detected)
How do you compute the attention selectivity index? And what is it?
The attention selectivity index tells you how much attending to some stimulus inside the RF increases neuron activity. 0 means no increase, positive means attending increases activity, negative means attending decrease activity. Essentially, it measures how much paying attention to something boosts activity.
(R in - R out) / (R in + R out)
** this index confirms that attention boosts activity in a positive way **
What is the saliency map in the brain? How did we check this?
In one case, participants just had to move their eyes from one position to another (single saccade task). In the single saccade task, the stimulus was in the RF but was behaviorally irrelevant (experiment was set up such that the stimulus had no actions associated with it).
The results are what you would expect, where the salient task triggers spiking activity in the LIP neurons, and the non-salient condition does not:
*This shows us that LIP neurons only respond to behaviorally salient stimuli.
What are the differences between within/outside RF and task-revelant vs task irrelevant? In relation to the salient task attention study.
Within RF: Tasks may involve stimuli presented within the neuron’s receptive field in LIP. Researchers examine how attention influences neural responses when stimuli are presented at the neuron’s preferred location.
Task Relevant: Neural responses are recorded while the animal performs a task in which attention is directed to specific stimuli or features.
What is the connection between the FEF and voluntary attention? What was the experiment that tested this?
the FEF can be microsimulated to lead to a specific location. one can bias attention by stimulating FEF without explicitly causing a saccade.
The experiment here was a luminance change detection task, where monkeys are shown a light source and asked to perform an action when they perceive the brightness (luminance) of the light having changed.
Results: sub-threshold stimulation does have positive effects on attentional sensitivity (less luminance change is needed to be detected) – only the case in the relevant region motor field. This suggests that FEF is also connected in some form to attention at large, and as that is connected to saccades and visual perception, this seems to be consistent with the saliency map theory mentioned above.
What was the task that showed fifferent brain regions seem to be active under endogenous vs exogenous attention
Participants were told which cue to pay attention to (endogenously) and at that cued location. Distinct networks were engaged by attention-directing cues versus subsequent targets, where subjects indicated whether there were grey checks in target (exogenous direction of attention).
Results: recorded the activity to target and cue. Found voluntary directing attention activates the superior frontal, inferior parietal, and the superior temporal regions based on cue. Different areas activated for target.
What is spatial hemineglect? Why is left hemineglect more common?
damage to the right inferior parietal lobule (IPL) (red) and the temporoparietal junction (TPJ shown as black) causes people to be unable to visually perceive one side of the visual field.
left hemineglect is more common than right hemineglect, simply because the former is more closely associated with exclusively the right hemisphere, whereas the latter is more connected to both hemispheres
