On the output of encoding during stimulus fixation

When subjects first fixate a degraded signal which is then compared with a subsequently fixated intact signal, an increase is observed of same/different latency — measured as the time elapsing between fixation of the second signal and the response — in comparison with the condition where both signals are intact. Four possible explanations of this effect are tested in two experiments. First, processing the first signal may still continue during fixation of the second one. Second, a degraded first signal could lead to a reduced feature set which might require “deeper” processing of the second intact signal to enable the match. Third, processing a signal may stop when a minimal code is acquired but, when comparing two signals, this only suffices when comparable codes can be obtained for both signals. Finally, matching two signals may be based on a comparison of all perceptual features, relevant and irrelevant alike, the efficiency depending on the similarity of the feature sets. A match between two successively fixated degraded signals occurs faster than when the first signal is intact and the second is degraded. Physical and name coding requirements of the match, did not influence the fixation time of the first signal but only the fixation time of the second signal. Together these results suggest comparison of all perceptual features in a matching task, relevant as well as irrelevant, with a faster outcome as the signal properties are more similar.