Pistorius has a "split personality", defence lawyer Kenny Oldwadge told the court. There are "two Oscars", he said -- a world-class athlete and a highly vulnerable individual with a serious disability.
Lawyers defending the 27-year-old on charges that he deliberately shot and killed model Reeva Steenkamp on Valentine's Day last year are calling their final witnesses.
Medical expert Wayne Derman testified that Pistorius, known as the Blade Runner for his j-shaped prosthetic limbs, was not always the fearless superhero depicted in sports advertisements.
"You have got a paradox," he said, .
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"Of an individual who is supremely able and an individual who is significantly disabled."
During five months of the stop-start trial, Pistorius's lawyers have sought to portray him as manically obsessed with safety after a difficult childhood with a mother who intermittently abused alcohol and in the face of high crime levels in South Africa.
Derman, who has known Pistorius for six years, testified that the runner is conditioned to "react through auditory stimulus" a result of training to starter pistols fired at the beginning of athletic races.
The expert witness, expected to be the last before the defence concludes its case, said it was Pistorius's unusual "startle magnitude" that "culminated in this horrific tragedy."
Prosecutors claim Pistorius killed Steenkamp following a row, arguing that neighbours living close to him heard a woman screaming the night he shot the model.