Inhibitory Control PDF

11/15/2024 Inhibitory Control Inhibitory control: Suppression of thoughts or actions that are no longer requ...

11/15/2024 Inhibitory Control Inhibitory control: Suppression of thoughts or actions that are no longer required or that are PSY 376 inappropriate in a situation Attention and Cognitive Control Considered to be a hallmark of cognitive control, supporting flexible and adaptive behavior Inhibitory Control Example (thought): Trying not to remember a bad day Example (action): Stopping your car when a traffic light turns red 1 2 1 2 Response Inhibition Stop Signal Procedure Response inhibition: Deliberately stopping a Response inhibition can be studied in the lab motor response with the stop signal procedure Typically involves interrupting Subjects perform a primary task (“go task”) on an ongoing action or activity most trials, responding to stimuli Real-world example: Stopping – Example: Categorizing a shape as square or yourself from stepping into a circle by pressing left or right keys busy intersection A stop signal is presented during some trials, Laboratory example: Stopping indicating the response should be withheld yourself from pressing a – Example: A tone as an auditory stop signal response key when instructed – Stop signal delay (SSD): Time from go stimulus 3 onset to stop signal onset 4 3 4 Stop Signal Procedure Stop Signal Procedure Stop signals randomly occur on a minority of trials (e.g., 25%) Therefore, subjects respond to the go stimulus on most trials Instructions to subjects: Respond as quickly and accurately as possible to the go stimulus when no stop signal occurs Withhold the response on stop signal trials, but do not wait for the stop signal to occur 5 – Trial ends automatically after a delay 6 5 6 1  11/15/2024 Stop Signal Procedure Stop Signal Procedure Dependent measures: Probability of responding to a stop signal Go reaction time (go RT) (failing to stop) is affected by SSD – Time to respond to the go stimulus – RT is variable, producing a go RT distribution Short SSD (stop signal soon after stimulus) Probability of stopping, p(inhibit|signal) Easy to stop; go task processing has not finished – Proportion of stop signal trials on which the p(respond|signal) is low response was successfully inhibited Probability of responding, p(respond|signal) Long SSD (stop signal long after stimulus) – Proportion of stop signal trials on which there Hard to stop; go task processing has finished and was a failure to inhibit the response response execution might be in progress p(inhibit|signal) + p(respond|signal) = 1.0 7 p(respond|signal) is high 8 7 8 Stop Signal Procedure Balancing Going and Stopping By measuring p(respond|signal) at varying Success in the stop-signal procedure involves SSDs, an inhibition function can be obtained balancing competing task demands Going fast improves RT on most trials but makes it harder to stop when needed Long SSD: Higher value Hard to stop Short SSD: means more failures to stop Easy to stop Response strategies can be adjusted to yield a tradeoff between going and stopping Proactive adjustments are made before a trial Reactive adjustments are made after a stop (Inhibition functions for each of three subjects doing a letter categorization go signal trial task with auditory stop signals; data from Logan & Cowan, 1984) 9 10 9 10 Proactive Adjustments Proactive Adjustments One strategy to increase stopping success is Lappin and Eriksen (1966) results to prolong go RT when SSD increases Go RT became longer as SSD increased, suggesting a proactive Lappin and Eriksen (1966) study response strategy adjustment Two lights in front of subject Go task (simple reaction): Press a (Respond) Even with the adjustment, stopping key when one light is turned on failures [p(respond|signal)] still Stop signal: Both lights turned on increased with SSD, despite SSD: Time between lights turning instructions to maintain a constant on (0, 12, 33, or 63 ms) (Do not respond) rate of successful inhibition 11 12 11 12 2  11/15/2024 Proactive Adjustments Proactive Adjustments Do people adjust go task responding based Verbruggen et al. (2006) results on the expectation of stop signals? Go RT longer when stop signals were expected than Verbruggen et al. (2006) study when they were not Go task: Categorize the letters Indicates subjects slowed making up a large block letter go task responding as a – Stimulus was congruent/incongruent proactive adjustment to One half of experiment: No stop signals improve stopping Other half of experiment: Stop signals (tones) on 30% of trials, SSD adjusted with tracking method 13 14 13 14 Reactive Adjustments Reactive Adjustments Do people adjust go task responding based Rieger and Gauggel (1999) results on stopping performance? Go RT longer after stop signal trial, regardless Rieger and Gauggel (1999) study of stopping outcome Go task: Classify a shape as circle or square by Indicates subjects pressing different keys adjusted go task Stop signal (tone) occurred on 25% of trials; SSD responding in reaction to stop signal adjusted using an alternative tracking method Examined go RT on current trial based on previous trial type 15 16 15 16 Reactive Adjustments Reactive Adjustments Verbruggen et al. (2008) study Verbruggen et al. (2008) results Go task: Classify a shape as circle or square by pressing different keys Longer go RTs after failures to stop suggest Stop signal (tone) occurred on 25% of trials; SSD reactive adjustments adjusted using the tracking method following errors Trials presented in pairs in which the stimulus Longer go RT after repeated or switched across trials in a pair successful stop only for Examined go RT on current trial based on stimulus repetitions previous trial type and stimulus transition suggests inhibition can be stimulus-specific 17 18 17 18 3  11/15/2024 Stop Signal Reaction Time Independent Race Model Stopping is not instantaneous: It takes time to SSRT can be estimated using the independent encode stop signal and inhibit response race model of Logan and Cowan (1984) Stop signal reaction time (SSRT): Time from Performance involves a race between a go stop signal onset to response inhibition process and a stop process Go process initiated by the go stimulus Problem: Stopping is a covert process Stop process initiated by the stop signal Unlike go RT, you cannot directly measure SSRT They “race” against each other and because there is no overt response when behavior is determined by the stopping is successful process that finishes first 19 20 19 20 Independent Race Model Independent Race Model Stop process finishes before go process: Model assumes go RTs are variable (resulting Successfully inhibit the response in a distribution), but SSRT has fixed duration More likely when SSD is short Go process finishes Stop process finishes before stop process before go process Go process finishes before stop process: (shaded area) (unshaded area) Fail to inhibit the response More likely when SSD is long Explains the inhibition function: As SSD gets The model correctly predicts the effects of longer, p(respond|signal) gets higher 21 prolonging SSD, SSRT, and go RT 22 21 22 Race Model: Prolonging SSD Race Model: Prolonging SSRT Short SSD Short SSRT Long SSD Long SSRT Longer SSD results in more inhibitory failure; Longer SSRT results in more inhibitory failure; p(respond|signal) is higher 23 p(respond|signal) is higher 24 23 24 4  11/15/2024 Race Model: Prolonging Go RT Race Model: Summary of Effects Short go RTs Prolonging SSD (stop signal comes later) or prolonging SSRT (stopping takes longer) Go process more likely to finish first, resulting in failure to inhibit the response Increase in p(respond|signal) Long go RTs Prolonging go RT (go task takes longer) Stop process more likely to finish first, resulting in successful response inhibition Longer go RTs result in more inhibitory success; Decrease in p(respond|signal) p(respond|signal) is lower 25 26 25 26 Race Model: Estimating SSRT Race Model: Estimating SSRT SSRT can be estimated with the integration Integration method: (You will not be tested on these details) method, which uses the go RT distribution, 1. Rank order the go RTs (shortest to longest) for SSD, and p(respond|signal) trials on which no stop signal occurs 2. Find the Nth go RT, where N is the proportion of go RTs corresponding to p(respond|signal) – Nth go RT cuts off the shaded area equal to p(respond|signal) in the previous figure – Example: For 100 go RTs and p(respond|signal) =.25, find the 25th fastest go trial 3. SSRT = Nth go RT – SSD 4. Repeat for each SSD and average across SSDs 27 28 27 28 Race Model: Estimating SSRT Race Model: Estimating SSRT SSRT can also be estimated with a tracking 3. Over time, the mean SSD will yield stopping method involving a dynamic SSD failures on about half of the stop signal trials: 1. Start with an initial SSD value (e.g., 300 ms) p(respond|signal) ≈.50 2. Adjust SSD (e.g., by 50-ms increments) after 4. SSRT = mean go RT – mean SSD every stop signal trial Estimates of SSRT are useful because they serve as indices of inhibitory control Longer SSRTs indicate slower stopping and result in higher probabilities of failing to stop, which might reflect changes or deficits in inhibitory 29 control 30 29 30 5  11/15/2024 Inhibitory Control Development Inhibitory Control Development How does inhibitory control Williams et al. (1999) results change across the life span? SSRT improves across childhood but changes Williams et al. (1999) study little in adulthood Subjects were 275 visitors to a science center Go RT improves across childhood but worsens (age range: 6–81 years) in adulthood Stop signal procedure with tracking method Suggests going and Go task: Press a key to classify a letter as X or O stopping develop and Stop signal (25% of trials): Brief auditory tone decline independently 31 32 31 32 Inhibitory Control Deficits Inhibitory Control Deficits Is deficient inhibitory control associated with ADHD characteristics: clinical and neurological disorders? Inattention: Difficulty maintaining attentional focus; mind wandering; lacking persistence Attention-deficit/hyperactivity – Not due to defiance or lack of comprehension Hyperactivity: Moving about constantly (even disorder (ADHD): A disorder when inappropriate); excessive fidgeting; marked by inattention and/or extreme restlessness hyperactivity/impulsivity that Impulsivity: Making hasty actions without interferes with functioning or thinking; difficulty delaying gratification; development intrusive or interruptive 33 34 33 34 Inhibitory Control Deficits Inhibitory Control Deficits ADHD diagnosis: Are people with ADHD impaired at stopping? Requires a comprehensive examination by a licensed clinician with expertise in ADHD Lijffijt et al. (2005) review of 29 studies Symptoms must be chronic, impair the person’s Each study involved a variant of the stop signal functioning, and cause the person to fall behind task, often with the tracking method and stop normal development for their age signals on 25% of trials – Symptoms not due to other medical conditions Each study compared subjects with ADHD vs. Symptoms can appear as early as 3 years of age normal subjects Typically diagnosed when a child is in elementary Also analyzed data by age, comparing children vs. school, but can be diagnosed in adulthood adults 35 36 35 36 6  11/15/2024 Inhibitory Control Deficits Inhibitory Control Deficits Lijffijt et al. (2005) results Schachar et al. (2005) study Children with ADHD had longer go RT and SSRT Stop signal procedure with tracking method compared with normal children Go task: Press a key to classify a letter as X or O – Slower going and stopping suggests a general Stop signal (25% of trials): Brief auditory tone attention deficit (not necessarily inhibitory) Compared three groups of subjects: Adults with ADHD had longer SSRT but – ADHD-concordant sibling pairs: Siblings both equivalent go RT compared with normal adults diagnosed with ADHD – Impaired stopping but no difference in going – ADHD-discordant sibling pairs: One sibling indicates a selective deficit in inhibitory diagnosed with ADHD; the other not control – Healthy controls: Neither they nor any siblings 37 diagnosed with ADHD 38 37 38 Inhibitory Control Deficits Inhibitory Control Deficits Schachar et al. (2005) results Other disorders that yield prolonged SSRT, SSRT elevated for all suggesting inhibitory control deficits: children with ADHD Obsessive-compulsive disorder (OCD) (first 3 bars) vs. Trichotillomania (repetitive hair pulling) healthy controls Tourette’s syndrome Unaffected siblings had intermediate Substance abuse linked to prolonged SSRT in: SSRT, suggesting a genetic component Chronic cocaine users to inhibitory deficits Chronic methamphetamine users Alcoholics 39 40 39 40 Summary of Inhibitory Control Stop signal procedure is an effective method for studying inhibitory control Proactive and reactive adjustments may occur to balance going and stopping Independent race model allows estimation of SSRT for the covert stopping process SSRT is a useful index for assessing inhibitory control, especially in clinical disorders 41 41 7