TASK 1 Flashcards
DRIFT DIFFUSION MODEL
decision making process that slowly accumulate evidence about the nature of the stimulus is reflected.
Evidence in favor of a particular goal gradually accrues as a random walk until it surpasses a threshold at which time a goal is selected, and a movement is generated
More than one goal: evidence in favor of each alternative is accumulated and diffusion processes race against each other until one of the reaches a threshold (winner) and determines the outcome
Evidence that continues to accumulate after movement onset occasionally leads to a mid-movement change of mind
There are 6 processes in movement generation. 3 “what processes” and 3 “how processes”. Some of these processes may occur in parallel.
Observe environment and identify potential targets
by using attention, select the target of interest
Task rules or constraints are applied
create motor goal
motor planning processes (action selection) define how the movement will be produced
for complex movements (need to overcome obstacle, …), abstract kinematics are applied that specify a particular trajectory before the appropriate action can be selected
generation of complete set of motor commands that produce the desired movement (movement specification)
Formation of motor goals: defining “what”
This process includes making decisions about the object’s location in the environment (which involves the deployment of attention), the application of task constraints (i.e., rules) to identify the motor goal, and the choice of whether to initiate the action.
fef and diffusion model
The FEF is associated with specifying motor goals rather than motor planning. With the evidence the FEF accumulates, the motor goal can be specified.
FEF is the only brain region that represents the transition from decisions about the stimulus to decisions about the motor action. Neural activity in FEF initially represents several alternative target choices and task-relevant stimulus features, but evolves over time to reflect only the final motor goal. Thus, FEF appears to be a site in which information about the attentionally selected object of interest is transformed—via the application of appropriate task rules—into a goal about the desired location to which a movement should be directed.
Action selection vs. movement specification (how)
Action selection vs. movement specification: the distinction between those processes is evident in neural activity from ventral premotor cortex (PMv), dorsal premotor cortex (PMd) and M1, where PMv reflects more abstract movement plans, independent of posture
Movement specification:
M1 and dorsal motor cortex are responsible for this.
Dorsal stream
= mediates navigation and the visual control of skilled actions directed at objects in the visual world
Includes interconnected extrastriate cortical areas in the parietal cortex, including medial superior temporal (MST), fundus of the superior temporal (FST), superior temporal polysensory (STP), ventral intraparietal (VIP), lateral intraparietal (LIP), mesial intraparietal area (MIP), anterior intraparietal (AIP) and inferioparietal area PF. There is however evidence for further anatomical and functional subdivisions exist
Ventral stream
Ventral stream = transforms visual inputs into representations that embody the enduring characteristics of objects and their spatial relationships
The ventral and dorsal stream process the same set of visual attributes, but for different behavioural goals
Dorso-dorsal stream
Dorso-dorsal stream = concerned with the control of action “online” (ongoing actions)
Most direct (immediate) visual pathway for action (primary and fast)
V3a to V6 to V6a and MIP (medial intraparietal sulcus) to dorsal pre-motor areas
Bilateral
Damage to this pathway results in optic ataxia (OA), We can therefore say that the dorso-dorsal stream is responsible for goal-directed visuo-motor transformations involving short-lived processes
Ventro-dorsal pathway
concerned with space perception and action understanding (recognition of actions made by others)
Medial superior temporal lobe (MT/MST) to inferior parietal lobule (IPL) to ventral pre-motor cortex
Left-lateralized (left IPL play role in making inferences about the function of an object from its structure)
This substream is therefore an interface between the other 2 streams. (dorsal & ventral stream )
Lesions to this stream lead to impairments of more cognitive aspects of action (those that require knowledge of skilled use). These deficits are often a part in limb apraxia (LA). Damage to inferior parietal lobe
grip & use system
While the grasp system only maintains information for seconds (it is based on current visual information which changes rapidly), the use system maintains information longer (it is based on conceptual knowledge).
initiation times for structure-based actions (grasping) were only slower for conflict- than non-conflict objects when participants had performed function-based actions (using) on the same objects in earlier blocks. This is because the use system (ventro-dorsal pathway) takes longer.. If we have activated the use pathway, the movements activated in this pathway interfere with the movements that are activated in the other pathway.
Therefore, we can state that the 2 pathways are not independent of each other: the use pathway is able to interfere with the grasp pathway but not so much the other way around.
Use actions are located more inferiorly in the parietal lobe than grasp actions. The locus of use actions is (neuroanatomically) close to other types of semantic representations concerning manipulable objects
it seems that only use but not grasp actions are intrinsic to words’ conceptual representations.
The automaticity debate
Viewed together, the evidence suggests that in the absence of a prepared manual response, function-based actions may be evoked either from object names or visual images. Structure-based actions, on the other hand, are evoked upon visual object presentation, but are not likely to be activated from object names unless an appropriate verb (e.g., ‘‘pick up’’) is provided or an object-relevant manual response is prepared
Word meaning (name of object) includes only function-based but not structure-based actions (words are understood without entailing action activation)
self generated movement
Findings have shown that neurons in the SMA, anterior cingulate sulcus and pre-motor cortex fire earlier on self-initiated movements. In monkeys where the pre-SMA, SMA and cingulate sulcus were removed, few self-initiated movements were made but externally triggered behavior was unaffected.
Only lesions to medial frontal cortex inhibit self-initiated actions, specifically lesions to pre-SMA and SMA
however…
Experiments show that there is activation in the SMA and pre-SMA, as well as in the cingulate motor areas, during externally triggered movements. In other words, activation of these areas is not confined to self-initiated movements. However, it can be shown with time-resolved fMRI that the activation in the pre-SMA and SMA starts earlier when the movements are self-initiated rather than externally triggered.
Activity in SMA and pre-SMA
Activity in SMA and pre-SMA reflects preparation for actions
anterior cingulate sulcus
anterior cingulate sulcus (and orbital frontal cortex) that encode the value of goals in terms of their probability, payoff and cost
The anterior cingulate sulcus is only involved in switching between actions when no external cue specifies a switch. It is therefore involved in the evaluation of outcomes
