epson scan - do levels adjustment at scan time yield any more infothan post-scan level adjustments?

Ok, a slightly technical question. If I use Epson Scan (or any other
simialr scaning software) to scan a photo, and change the levels (e.g.
brightness, contrast, or gamma) before doing the scan proper, does the
scanner:

a) somehow adjust its sensitivity to light during the scan process and
hence genuinely alter the information it picks up
b) just apply the levels to the scanned image, after the scan, in a
manner which I might as well just do in photoshop etc?

alex