Abstract
When a target is preceded and/or succeeded by other irrelevant stimuli (distractors) its identification is impaired. Depending on inter-item intervals (SOAs), this impairment is defined as temporal crowding (SOA=170-475ms) or ordinary masking (SOA <150ms). Here, we examined the nature of the impairment brought about by these phenomena using the same stimuli and estimation task. This allowed us to directly compare their effects on the precision of target encoding, guessing rate, and substitution errors, as well as examine how these two phenomena are affected by target-distractors similarity. The participants viewed a sequence of three oriented stimuli. The target was the second stimulus, and the task was to reproduce its orientation. Depending on the experiment, the SOAs were either long (crowding) or short (masking), and the target and distractors had a similar or different luminance. Luminance differences were either fixed throughout the experiment or varied randomly. With temporal crowding, we found a significant SOA effect on the variance with which the participants reported target orientation, but there was no significant effect on the guessing rate. With masking, we found a significant SOA effect on the guessing rate but not the variance. These findings suggest that temporal crowding impairs encoding precision but has no effect on the signal-to-noise ratio (SNR), whereas masking decreases the SNR but has no effect on encoding precision. Both affected substitution errors, but in a different manner. Furthermore, the effect of target-distractors similarity also depended on the phenomenon. With crowding, when the luminance-difference was fixed, substitution errors decreased, but when it varied, this reduction was no longer evident, rather an increased precision emerged. Finally, with masking, only the SNR was affected. Thus, different mechanisms seem to mediate temporal crowding and masking, and although target-distractors similarity modulated the impairment observed with both phenomena these modulations likely occur at different levels.