Example 1: The Attentional Blink Raymond, Shapiro, & Arnell (1992) T2 Detection Accuracy
What Causes the Blink? Are subjects unable to perceive T2 during the AB? Are subjects unable to perceive T2 during the AB? -Or do they see it and fail to remember it? Previous research shows that we can perceive even complex pictures at 8/sec Previous research shows that we can perceive even complex pictures at 8/sec -We ought to be able to perceive letters at 10/sec Logic of study Logic of study -Early sensory suppression during AB (P1 & N1)? -Late perceptual suppression during AB (N400)? -Postperceptual working memory suppression (P3)?
Experiment 1: P1 and N1 T1 Task: Digit Odd or Even? T2 Task: Red item Vowel or Consonant? Prediction: No P1/N1 suppression during AB
Experiment 1 Results
Difficult to draw strong conclusions from the lack of an ERP effect
Experiment 2: N400 How to demonstrate that T2 was fully identified? How to demonstrate that T2 was fully identified? -Show that it can elicit an N400 Sweet …. Sugar Hot …. Sugar If a semantic mismatch is detected when T2 is a word, then T2 must have been fully identified If a semantic mismatch is detected when T2 is a word, then T2 must have been fully identified
Experiment 2: N400
The Overlap Problem
Experiment 2 Results
Does it matter whether this is really an N400? Strategy 8: Use a component to study the processes that precede it rather than the process that generates it
Experiment 3: Control Is N400 sensitive to modest changes in perceptibility? Does even a slight perceived mismatch cause a large N400?
Experiment 4: P3 Isolate P3 by subtracting frequent T2 from rare T2
Experiment 4 Results
Does it matter whether this is really a P3?
Recap of Strategies Strategy #1- Focus on a specific component Strategy #2- Use well-studied experimental manipulations Strategy #3- Focus on large components Strategy #4- Isolate components with difference waves Strategy #5- Focus on components that are easily isolated Strategy #6- Use component-independent experimental designs Strategy #7- Hijack useful components from other domains Strategy #8- Use a component to assess the processes that came before it
Additional Rules Rule #11- Never assume that the amplitude and latency of an ERP component are linearly or even monotonically related to the quality and timing of a cognitive process. This can be tested, but it should not be assumed. Rule #12- Don’t forget about behavior in ERP experiments. Dissociations between behavior and ERPs are sometimes troubling, but they are often informative
Example 2: Schizophrenia Typical schizophrenia ERP task- Auditory oddball Typical schizophrenia ERP task- Auditory oddball % standards of one pitch % targets of another pitch (count or press for targets) -Measure amplitude of P3 peak for rare stimuli Large, replicable reduction in P3 amplitude (d = 0.89) Large, replicable reduction in P3 amplitude (d = 0.89) But what does it mean? But what does it mean? Mathalon et al., 2000
P3 Latency in Schizophrenia RTs are typically ms greater in SC patients RTs are typically ms greater in SC patients -RTs often not reported in P3 studies (most use a counting task in which RT does not apply) P3 latency modestly greater in patients P3 latency modestly greater in patients -Often not significant Interesting: RT slowing + no substantial P3 slowing Interesting: RT slowing + no substantial P3 slowing Mathalon et al., 2000
A Different Approach The hardest part of ERP research is isolating specific components The hardest part of ERP research is isolating specific components -This is why we don’t have a very good theory of the P3 wave -Makes it hard to interpret a reduction in patient P3 amplitude Relevant strategies: Relevant strategies: -Isolate components with difference waves -Focus on components that are easily isolated -Use component-independent experimental designs -Use a component to measure the processes that necessarily precede it (focus on onset latency) Additional strategy: Additional strategy: -Take advantage of temporal resolution -Effect size = number of milliseconds!!!
Subtraction Approach Early Visual Processes Shifts of Attention Stimulus Categorization Stim/Resp Translation Response Execution Upper minus Lower Contra Target minus Ipsi Target Rare minus Frequent Contra Hand minus Ipsi Hand C1 N2pc P3 LRP RT STAGESUBTRACTIONCOMPONENT Luck et al., 2006
P3 and LRP N2pc is not delayed in schizophrenia N2pc is not delayed in schizophrenia Prior studies find little or no P3 delay Prior studies find little or no P3 delay But RT is typically delayed by 100+ ms But RT is typically delayed by 100+ ms Then what is delayed? Then what is delayed? -Stimulus/response translation (response selection)? -Response initiation and execution? To test, examine P3, LRP, and RT To test, examine P3, LRP, and RT (with Jim Gold, Becky Fuller, Emily Kappenman)
P3 Latency P3 amplitude depends on the probability of a task-defined stimulus category P3 amplitude depends on the probability of a task-defined stimulus category P3 effect cannot occur until after categorization P3 effect cannot occur until after categorization P3 latency is tied to the amount of time required to perceive and categorize a stimulus (“stimulus evaluation time”) P3 latency is tied to the amount of time required to perceive and categorize a stimulus (“stimulus evaluation time”)
Lateralized Readiness Potential (LRP) More negative over contralateral cortex for hand movements More negative over contralateral cortex for hand movements LRP cannot be elicited until stimulus/response translation (response selection) has occurred LRP cannot be elicited until stimulus/response translation (response selection) has occurred But prior to completion of response programming But prior to completion of response programming Miller & Hackley (1992)
3 Methods Digit / Letter p =.80/.20 or p =.50/.50 Left Hand / Right Hand Duration = 200 ms SOA = 1500±150 ms Isolate P3 with Rare-minus-Frequent difference wave Isolate LRP with Contra-minus-Ipsi difference wave 3
Raw ERP Waveforms P3 amplitude difference for all probability levels No P3 latency difference Control RT Patient RT Parietal Electrode Sites
P3: Rare Minus Frequent No P3 amplitude difference No P3 latency difference No slowing of simple perception & categorization Difficult to know if this replicates previous research Parietal Electrode Sites
Response-Locked P3 Significant P3 onset latency difference Stimulus P3 not delayed Stimulus P3 not delayed Stimulus Response is delayed Stimulus Response is delayed Prediction: P3 Response should be delayed Prediction: P3 Response should be delayed Parietal Electrode Sites
Schizophrenia Summary Visual attention is normal Visual attention is normal -No increase in N2pc latency Categorization is normal Categorization is normal -No reduction in rare-minus-frequent amplitude -No increase in time from stimulus to P3 onset or peak -Increase in time from P3 onset to response Response selection is impaired Response selection is impaired -Substantial reduction of LRP amplitude -Increase in time from stimulus to LRP onset -Possible increase in time from LRP onset to response