Classic debates in selective attention: early vs late, perceptual load vs dilution, mean RT vs measures of capacity.

We briefly summarize two important debates regarding selective attention (early vs late selection; perceptual load vs distractor dilution). Also, we report the results of an attempt to replicate Lavie (1995, Journal of Experimental Psychology: Human Perception and Performance 21 451-468). We suggest that measures capable of characterizing the capacity of information processing systems (compared to reporting only mean reaction time) could add great clarity to this literature.

Effects of perceptual load on startle reflex modification at a long lead interval.

Inhibition of the startle eyeblink response at long lead intervals has been hypothesized to occur when attention is directed away from the modality of the startle stimulus, particularly if attention is directed to a stimulus of high perceptual load. In a test of this hypothesis, participants performed a delayed-matching-to-sample task. On each trial a pattern of dots (the sample) was followed by a second pattern of dots (the target). The task was to say whether the sample and target patterns matched. Perceptual load was manipulated by varying the number of dots in the sample. Auditory startle stimuli were presented 1200 ms after onset of the samples. A linear increase in startle magnitude was found as the number of dots increased. The results are not consistent with the hypothesis that startle inhibition occurs when the lead and startle stimuli are in different modalities under conditions of high perceptual load.

Attention and prepulse inhibition: the effects of task-relevant, irrelevant, and no-task conditions.

We investigated whether attentional modulation of prepulse inhibition (PPI) is due to increased protection of processing of attended lead stimuli, decreased protection of processing of ignored lead stimuli, or a combination of both processes. Task and no-task trials, pre-cued by red and blue dots on a computer screen, were randomly intermixed. College student participants were instructed to do a tone duration judgment task on trials preceded by one color (task condition) and to do nothing on trials preceded by the other color (no-task condition). On task condition trials participants were instructed to count the number of longer duration tones of a particular pitch (attended condition) and to ignore tones of a different pitch (ignored condition). White noise startle stimuli were presented at 60 ms and 120 ms lead intervals on some trials in each condition. Additional startle stimuli were presented during the inter-trial intervals to measure baseline (unmodified) startle response. PPI in the attended condition was reliably greater than that in both the ignored and no-task conditions. PPI did not differ between the ignored and no-task conditions. The results are consistent with the conclusion that attentional modulation of PPI is due to increased protection of attended stimuli and not to decreased protection of ignored stimuli. Possible reasons for robust attentional modulation at the 60 ms lead interval as well as the usual 120 ms lead interval are discussed.