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What do we see when reading?

As visual acuity drops off rapidly from the point of fixation, only 4-5 letters are seen with 100% accuracy - perceptual span is 4 characters to the left, 15 characters to the right of fixation.


How is eye tracking achieved?

A low-level infrared light is picked up by a camera, determining where the pupil is.


What has eye tracking shown about fixations and saccades when reading English?

Eyes move from left to right 85% of the time and right to left (new line/going back) 15% of the time.


How long are fixations in English?

60-500ms, average 250ms.


Describe saccades in English.

They vary between one character and a whole sentence, with an average of 6-9 characters.


What are the early measures of reading time?

First fixation duration and first-pass reading time (for the word of interest).


What are the later measures of reading time?

Regression path and total reading time.


What can eye-tracking experimental designs do other than simply monitoring eye position?

They can be used to create gaze-contingent paradigms.


What are gaze-contingent paradigms?

Information is fed back to the computer, which changes the display - for example once an invisible boundary is passed a word can be changed.


What can gaze-contingent paradigms be used for?

Measuring preview effects - if the (non-)word 'evh' is initially presented, then changed to 'sat', compared to the sentence with the correct preview it takes 40ms longer to read - this is the preview benefit; the word is already processed to some extent before it's looked at.


What are the advantages of eye tracking as an experimental method?

It measures naturalistic behaviour, is non-intrusive, provides moment-by-moment indication of ease (or difficulty) of text comprehension, and allows the use of gaze-contingent paradigms.


What are the disadvantages of eye tracking as an experimental method?

It is labour intensive for the experimenter, there are training requirements, and it's expensive.


When using ERPs, what can cause EEG artifacts?

Blinks, muscle movements and eye movements.


How can the problem of EEG artifacts be solved?

By asking participants not to blink/move, presenting stimuli word-by-word, and removing from the data with algorithms. Participants should also read several hundred sentences to even out noise.


What are ERP components?

Predictable and identifiable waveforms which co-vary in response to experimental manipulations.


What are two language-related ERP components?

The N400 and P600.


What can ERP components be described in terms of?

Latency (after first seeing word), polarity (negative plotted upwards on graph, positive plotted downwards), and scalp distribution.


What is the N400 argued to reflect difficulty with?

Integrating words into context (sentence and discourse incongruity) and semantic retrieval (affected by word frequency and repetition).


What evidence is there that the N400 is related to integration of words into context?

1. Sentence incongruity: Kutas & Hillyard (1980) found that incongruous sentences cause ERP to shoot up (N400) relative to congruous sentences.
2. Discourse incongruity: Van Berkum et al. (1999) found that a sentence anomaly causes ERP to shoot up (N400) relative to a coherent sentence.


What evidence is there that the N400 is related to semantic retrieval?

N400 for less frequent words and small N400 for unrepeated words.


What is the P600?

A syntax-related ERP component.


In what cases is the P600 observed?

• Subject verb agreement (Hagoort, Brown & Groothusen, 1993) - grammatical error
- The spoilt child throws/throw the toy on the ground
• Syntactic ‘garden path’ sentences (Osterhout, Holcomb & Swinney, 1994) - complex grammatical structure
- The professor saw (that) the student would succeed


What are the advantages of ERPs?

They're a non-invasive technique that measures neural activity in real time. Measures are ‘time-locked’ to a critical event, and different components can reflect different underlying cognitive processes, unlike eye-tracking which only shows difficulty.


What are the disadvantages of ERPs?

- Unnatural word-by-word stimulus presentation
- Hard to tell ‘where’ in the brain processes occur
- EEG artifacts can be difficult to remove
- Labour intensive/expensive/training requirements