To elucidate the roles of visual areas V1 and V2 and their interaction in early perceptual processing, we studied the responses of V1 and V2 neurons to statically displayed Kanizsa figures. We found evidence that V1 neurons respond to illusory contours of the Kanizsa figures. The illusory contour signals in V1 are weaker than in V2, but are significant, particularly in the superficial layers. The population averaged response to illusory contours emerged 100 msec after stimulus onset in the superficial layers of V1, and around 120 -190 msec in the deep layers. The illusory contour response in V2 began earlier, occurring at 70 msec in the superficial layers and at 95 msec in the deep layers. The temporal sequence of the events suggests that the computation of illusory contours involves intercortical interaction, and that early perceptual organization is likely to be an interactive process. W hen viewing the Kanizsa display shown in Fig. 1a, we perceive the borders of a square even in regions of the image where there is no direct visual evidence for them. This is one example of the phenomenon of illusory or subjective contours (1). This perceptual phenomenon has been reported by von der Heydt and colleagues (2, 3) to possess a direct physiological correlate in macaque area V2, where some neurons were found to respond to an illusory contour moving across their receptive fields. In contrast, they failed to observe responses to illusory contours in area V1. The apparent absence of illusory-contour responses in area V1 is puzzling both because there are recurrent pathways from V2 to V1 and because interaction between modules is a key feature of many models for early perceptual organization (4-7). Moreover, other groups have shown that neurons in area V1 do detect subjective contours defined indirectly in other ways, for example by the fracture line where lines or out of phase sine wave gratings abut (8, 9). Because of the nature of their stimuli, these studies (8, 9) did not resolve the question of whether their results would apply to the illusory contours as studied by Von der Heydt and colleagues. In light of these considerations, we decided to reexamine the issue of neural responses to illusory contours in areas V1 and V2. By using a technique designed to call attention to the illusory square and employing a static display that allowed tracking the temporal evolution of responses, we have found that neurons in area V1 do respond to illusory contours, although at a latency greater than that in V2.We conducted the following neurophysiological experiment on two awake behaving rhesus monkeys. In each trial, while the monkey was fixating a red dot on the screen within a 0.5°fixation window, a sequence of four stimuli was presented. The presentation of each stimulus in the sequence lasted for 400 msec. On completion of the sequence, the monkey had to make a saccadic eye movement to another red dot that appeared at a random position on the screen to complete the trial. The set of test stimuli included a Kanizsa figure with...

This paper presents a study on Hierarchical Surrogate-Assisted Evolutionary Algorithm (HSAEA) using different global surrogate models for solving computationally expensive optimization problems. In particular, we consider the use of Gaussian Process (GP) and Polynomial Regression (PR) methods for approximating the global fitness landscape in the surrogateassisted evolutionary search. The global surrogate model serves to pre-screen the EA population for promising individuals. Subsequently, these potential individuals undergo a local search in the form of Lamarckian learning using online local surrogate models. Numerical results are presented on two multi-modal benchmark test functions. The results obtained show that both PR-HSAEA and GP-HSAEA converge to good designs on a limited computational budget. Further, our study also shows that the GP model is suitable for global surrogate modeling in HSAEA if the evaluation function is very expensive in computations. On moderately expensive problems, the PR method may serve to generate better efficiency than using GP.