There’s something creepy about the digital realism of thre computer enhanced movie “Polar Express.” But why? Perhaps things in the movie look too real? Or are they not real enough? “Stated simply, the idea is that if one were to plot emotional response against similarity to human appearance and movement, the curve is not a sure, steady upward trend. Instead, there is a peak shortly before one reaches a completely human “look” . . . but then a deep chasm plunges below neutrality into a strongly negative response before rebounding to a second peak where resemblance to humanity is complete.”