Gratton & Fabiani (2001)

 Hemodynamic techniques:  PET and fMRI useful for spatial information about neural activity  Electromagnetic techniques:  EEG and MEG useful for temporal information about neural activity

 Hemodynamic techniques lack temporal specificity and electromagnetic techniques lack spatial specificity.  EROS provides both, good temporal and spatial information.

 Fiber optic cables act as sources and detectors.  Sources have just one fiber, detectors have many.  Sources carry light from lasers or LEDs.  Photomotopliers function as detectors of photons.

 If photons are emitted from a light-source (fiber optic) against the surface of a semi-infinite, homogenous object they can be modeled using the same equations as those that describe the positive half of a dipole.  Depth in the case of EROS depends partially on the distance between the source and detector.

 As light propagates from the source it gets scattered and absorbed by brain tissue.  Changes in the activity of brain tissue affect the amount of scattering and absorption.  Scattering causes the photons to have a longer transit time from source to detector. ▪ Therefore, scattering (activity) can be estimated from the increase in transit time/phase delay.

Intensity Time Input Output

 Visual stimulation experiment shows transit time increase for activated areas mm apart.

 Comparison found good temporal and spatial overlap with ERPs and fMRI.

 Changes in neuronal membrane affect transparency of membrane and diffraction.

 Neuronal membranes distend/shrink as ions + H 2 O move in/out after an action potential.

 Pros:  Good temporal resolution (milliseconds)  Good spatial resolution (<1cm)  Useful for studying neurovascular coupling  Cons:  Penetration from scalp is limited to 3-5cm (cortex)  Low signal-to-noise ratio requires averaging ▪ Marianna’s question #1 ▪ Pulse correction, phase rejection, movement artifact

 CNL EROS Video CNL EROS Video

Tse, Lee, Sullivan, Garnsey, Dell, Fabiani and Gratton (2007)

 How do the temporal cortex and inferior frontal cortex interact?  fMRI is too slow to view this interaction  Does processing differ for syntactic vs. semantic anomaly?  Can EROS image interactions between cortical areas?

IIdentifies three functional components: MMemory: store of language information, involved in retrieval  U Unification: integration of lexically retrieved information  C Control: language to action, such as choose between using one of two languages C U M

 Increased response in left inferior frontal when unification load is increased (in response to anomalous critical word). A lesser response also occurs for correct sentences.

 Model emphasizes that posterior and dorsal areas integrate syntactic information, while anterior and ventral areas function more for semantic integration.  But, there is a lot of overlap.  Preview of Albert’s question  Little evidence extending this functional specialization to the temporal lobe.

 16 participants  All right-handed native English speakers  11 females and 5 females, ages  Lucy’s question:  Why the disproportionate # of females?  Control for sinistrality?

 Each participant saw 864 sentences  336 unacceptable sentences ▪144 were semantically anomalous at the final word  “The hungry child ate the floor.” ▪48 filler sentences contained semantically anomalous words in medial position to prevent expectations that anomalies only occur in the final position ▪96 had grammatical violations of subject verb agreement ▪ “If work isn’t done, it pile…” ▪48 had grammatically incorrect pronoun case ▪ “My mother promised to buy I…”

 528 acceptable sentences  144 controls for the semantic sentences  96 for syntactic subject verb agreement  48 for pronoun case anomaly  240 sentences to ensure subjects expect most sentences to be acceptable  Length and frequency was accounted for across conditions.  Israel’s questions-  Couldn’t syntactic anomaly be sentence-final? (When it rains, it pour(s)”  How long is the experiment? ▪Approx. 10 hours total broken up into two 5-hour sessions.

 Sentences were presented word-by- word at the center of screen and subjects had to judge if sentence was well- formed.

 ERPs were recorded.  EEG recording used four scalp electrodes (Fz, Cz, Pz, and right mastoid). ▪ Final bandpass filter of Hz ▪ Sampled at 100Hz ▪ Time-locked 1500 ms epochs with 200ms pre-stimulus onset

 EROS recording used two montages. ▪ Laser diodes emitted 830nm light at 220MHz which was picked up by PMTs modulated at ~220MHz  Sources, detectors, nasion, preauricular points and random points were digitally localized using a Fastrak 3D digitizer.  Coregistration with individual subject’s anatomy provided by MRI.

 128 source-detector pairs per montage

 Most sentences were classified correctly:  Semantically acceptable- 94%  Semantically unacceptable- 95%  Syntactically unacceptable – 86%  Syntactically acceptable- 88%  Analyses were performed only on these correct trials.

 Semantic unacceptable – acceptable  Difference waveform computed from ms peaking at 420ms (p<.001)

 Syntactically unacceptable – acceptable  Difference waveform computed from peaking at 860 ms (p<.001)

 Significant increase in phase delay for anomalous critical words.  Both conditions elicited S/MTC activation followed by IFC activation.  Pattern occurred a few times for semantic condition suggesting oscillatory behavior.  ROIs analyzed independently

 Different areas activated for each condition up to ~665ms.  Semantic = ventral anterior/middle  Syntactic = dorsal posterior temporal  More frontal activation for semantic anomaly, but lots of overlap.  EROS signals predicted the N ms in S/MTC) and P ms, 914ms in IFC)in semantic and syntactic condition, respectively, but not vice versa.  Double dissociation in EROS/ERP

 Contrasts were 17mm apart along inferior - superior, but not anterior-posterior  After 655ms there was no reliable differences between the activity for contrasts.  Albert’s question ▪ Potentially due to response ▪ Hagoort’s model

 EROS successfully showed interaction between temporal-frontal network involved in language processing.  Supports model in which retrieval occurs in the temporal regions and the integration occurs in the frontal regions.

 Might reflect integration process in IFC in which predictions about upcoming words are generated and sent to temporal areas.  Marianna’s question # 1  Lucy’s question # 1 & 2  Lynn’s Question  Since syntactic anomalies were relatively easy to rectify there was little frontal activity.  Semantic anomaly more difficult to correct and hence more back and forth. ▪ More extensive frontal activity ▪ Double checks retrieval?  The location of these networks is consistent with previous fMRI studies.

 Syntactic words were in medial position while semantic were final.  Is activation comparable for sentence medial and sentence final positions?

Effect is still present just smaller, as is usually the case.