Box 1.

Various settings for VEP

(In full compliance with the recommendations of the International Federation of Clinical Neurophysiology (IFCN) Committee[14])

Recording conditions:

1. Filter: Low cutoff (high pass): 1–3 Hz High cut off (low pass): 100–300 Hz

2. Amplification between 20,000 and 1,00,000

3. Sweep duration between: 250 and 500 ms

4. Number of epochs: at least 100 were averaged

5. Electrode impedance was kept below 5 kohms.

Stimulation options:

1. Black and white checker board

2. Distance between subject and screen: 70–100 cm

3. Contrast: 50%–80%

4. Fixation point for full field size greater than 8°

5. Size of pattern element: 8 × 8 mm.

6. Rate of stimulation: For transient VEP: 1 Hz For steady state VEP: 4–8 Hz

7. Mean luminance of the central field: 20–40 cd/m2

Background luminance: 20–40 cd/m2

Two channels (as per 10–20 international system)

1. Channel 1: Oz–FPz

2. Channel 2: Oz–A1A2 (linked ear)

Ground electrode position at: Cz