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.

Inte

nsity

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 + H2O 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

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?

Identifies three functional components: Memory: store of

language information, involved in retrieval

Unification: integration of lexically retrieved information

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 18-30

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 0.1-20Hz▪ 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 200-500ms peaking at 420ms (p<.001)

Syntactically unacceptable –acceptable Difference

waveform computed from 500-1500 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 N400 (@179ms, 384ms in S/MTC) and P600 (@ 819ms, 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.