Iterations are also referred to in the literature as “time-step” (Braun,
1999) or “gist” (Joubert, Rousselet, Fize, & Fabre-Thorpe,
2007). It was argued earlier that presentation time is an important constraint for models in which contour salience results from an iterative computation, suggesting approximately 30 ms per time-step (Braun, Niebur, Schuster, & Koch,
1994a). Although this is far more that is needed for synaptic transmission, which is all that is postulated by some models of contour salience (Li,
1998; Pettet et al.,
1998), it is just barely enough for establishing temporal synchronicity (Yen & Finkel,
1998), or for triggering NMDA-mediated plasticity (Braun et al.,
1994a). The benefit of contour detection from longer durations of presentation was reported. Although detection was possible even for 80-ms durations (Polat & Bonneh,
2000), it deteriorated with the decrease of the presentation duration, which was directly compared by Field and colleagues (
1993). In fact, it was much noisier for 250 than for 1000-ms durations. Moreover, a gist of a scene could be extracted with high accuracy (94% correct or more) from images that are flashed for about 20 ms by human observers (Delorme, Richard, & Fabre-Thorpe,
2000; Fabre-Thorpe, Delorme, Marlot, & Thorpe,
2001; Fabre-Thorpe, Richard, & Thorpe,
1998; Joubert et al.,
2007; Rousselet, Macé, & Fabre-Thorpe,
2003; Thorpe, Fize, & Marlot,
1996; VanRullen & Thorpe,
2001). In our model, each iteration may represent a successive gist extraction, provided by longer presentation times that are typically allowed in the contour integration studies.