( We ( ( ( define ON ) ( ( detectors ( as ( motion detectors ) ) ) ( that ( ( ( ( respond ( to ( positive ( contrast changes ) ) ) ) ( -LRB- ( ( that ( is ( from ( dark ( to bright ) ) ) ) ) -RRB- ) ) ) , ) ( ( OFF detectors ) ( respond ( to ( negative ( contrast changes ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VB define) (PRT (RP ON)) (NP (NP (NNS detectors)) (PP (IN as) (NP (NN motion) (NNS detectors))) (SBAR (WHNP (WDT that)) (S (VP (VBP respond) (PP (TO to) (NP (JJ positive) (NN contrast) (NNS changes))) (PRN (-LRB- -LRB-) (SBAR (WHNP (WDT that)) (S (VP (VBZ is) (PP (IN from) (ADJP (JJ dark) (PP (TO to) (ADJP (JJ bright)))))))) (-RRB- -RRB-)) (, ,) (S (NP (NNP OFF) (NNS detectors)) (VP (VB respond) (PP (TO to) (NP (JJ negative) (NN contrast) (NNS changes)))))))))) (. .)))
We define ON detectors as motion detectors that respond to positive contrast changes (that is from dark to bright), OFF detectors respond to negative contrast changes.
(ROOT (S (PP (IN In) (NP (NN science))) (, ,) (NP (NN motion)) (VP (VBZ is) (VP (VBN defined) (PP (IN as) (NP (NP (DT a) (NN change)) (PP (IN in) (NP (NN position))))))) (. .)))