Attentional Blink - Temporary Suppression Of Visual Processing (Raymond, Shapiro, & Arnell, 1992) PDF

# Temporary Suppression of Visual Processing in an RSVP Task: An Attentional Blink? ## Authors - Jane E. Raymond - Kimron L. Shapiro - Karen M. Arnell - University of Calgary, Calgary, Alberta, Canada ## Abstract This paper studies the limits of the brain's ability to process a stream of stimuli...

# Temporary Suppression of Visual Processing in an RSVP Task: An Attentional Blink? ## Authors - Jane E. Raymond - Kimron L. Shapiro - Karen M. Arnell - University of Calgary, Calgary, Alberta, Canada ## Abstract This paper studies the limits of the brain's ability to process a stream of stimuli using rapid serial visual presentation (RSVP). Through RSVP, subjects are asked to identify a partially specified letter (target) and then to detect the presence or absence of a fully specified letter (probe). While targets are accurately identified, probes are poorly detected when presented during a 270-ms interval beginning 180 ms after the target. The presence of stimuli after the target but before target-identification processes are complete produces interference at a letter-recognition stage. This interference is a temporary suppression of visual attention, leading to a deficit in processing stimuli presented after the target, know as the "attentional blink". ## Introduction RSVP procedures can be categorized on the basis of the information available for target identification; target-identification tasks vs. detection tasks. - **Target-identification tasks**: This study aims to understand the limitations of the temporal characteristics of perceptual and attentional processes in identification through RSVP. - Subjects are asked to identify partially specified targets. For example, the target could be the only red letter in a stream of colored letters. - Subjects are then asked to report a to-be-reported characteristic. For example, the subject might be required to supply the letter name of the only red letter in the stream. - **Detection tasks**: Subjects are asked to detect the presence or absence of a fully specified letter (probe) presented at various intervals after the target. For example, the probe could be a black X embedded in a stream of black letters. ## Single-task RSVP Studies Single-task RSVP experiments (in which only one target is identified) have provided data that is useful in developing theories of the attentional and perceptual mechanisms that mediate such a task. - **Target-defining characteristic**: This is the feature that distinguishes the target from other items in the stimulus stream. For example, color or a letter's position within a stream of letters. - **To-be-reported feature**: This is the characteristic that is to be reported about the target. For example, the letter name. - **Single-task RSVP studies have shown that even with very rapid stimulus presentation rates, subjects are able to identify the target on a significant proportion of trials.** - This indicates that even with very rapid presentation rates, subjects are able to identify the target on a significant proportion of trials. - **When target-identification errors are made, however, they tend to be systematic.** - This allows for modeling the processes involved in target identification. - **Pretarget intrusions**: Naming the to-be-reported feature from an item immediately preceding the target by n items. - **Posttarget intrusions**: Naming the to-be-reported feature from an item succeeding the target by n items. ## Multiple-task RSVP Studies Multiple-task RSVP experiments have demonstrated that there is a significant cost to identifying the first target in a multiple-task RSVP experiment. - **This cost is a temporary but relatively long-lasting deficit in the identification of stimuli presented after the first target.** - This deficit is known as the "posttarget processing deficit." - **The present paper explores further the nature of this processing deficit.** - The goal is to determine the factors that underlie the deficit and to investigate the role of immediate posttarget stimulation on the production of the processing deficit. ### Experiment 1 The purpose of this experiment is to replicate one of the experiments reported by Weichselgartner and Sperling (1987), using slightly faster presentation rates (11 items/s rather than 10 items/s) and different stimuli (letters rather than digits). **The subject's tasks are:** 1. **Identify a white target letter embedded in a stream of black letters**. 2. **Identify the three letters presented immediately after the target letter**. - In Experiments 1 and 2, a stream of letters is presented to the subject for 90 trials. - Each trial consists of 7 to 15 pre-target letters, a target (white letter), and 8 post-target letters. - Letters are displayed for 15ms with an interstimulus interval (ISI) of 75ms. **Results:** - The target and the last letter in the stream are reported with the highest probability (.8). - Subjects rarely report items presented prior to the target. - The +2 and +3 items are reported with significantly less probability than the +1, +5, +6, and +7 items. These results replicate the posttarget processing deficit reported by Weichselgartner and Sperling (1987), indicating that in this situation, the effect is maximal during the interval between 180 and 270 ms posttarget. ### Experiment 2 This experiment asks two questions: 1. **Will performance on a simple probe-detection task be negatively affected by a prior target-identification task?** 2. **If so, is the posttarget processing deficit mediated by sensory or attentional factors?** **The experiment includes two conditions:** 1. **Experimental condition**: Subjects are asked to identify a white target letter embedded in a stream of black letters and subsequently respond whether an X (probe) had been presented in the posttarget letter stream. 2. **Control condition**: Subjects are told to ignore the target color and simply to respond whether the X had been presented in the posttarget letter stream. **Results:** - **Probe detection**: Subjects in the control condition correctly detected the probe on 85% or better of trials for all probe serial positions. In the experimental condition, probe detection dropped below 60% for the posttarget interval from 180 to 450 ms. This indicates a significant posttarget processing deficit, suggesting that the deficit is attentional, not sensory. - **Posttarget processing deficit**: The experimental condition revealed a significant posttarget processing deficit, suggesting that the deficit is attentional, not sensory. Sensory factors do not appear to play a significant role in the posttarget processing deficit. - **Target identification**: The results indicate that the posttarget processing deficit affects the mechanisms involved in letter recognition. The deficit is not due to difficulties in memory encoding or response demands. ### Experiment 3 This experiment aims to investigate whether the suppression mechanism identified in Experiment 2 is ballistic (non-adaptive) or event-related. **The experiment includes two conditions:** 1. **Experimental condition**: Subjects are first asked to identify a white target letter embedded in a stream of black letters and subsequently respond whether an X (probe) had been presented in the posttarget letter stream. 2. **Control condition**: Subjects are told to ignore the target color and are simply asked to respond whether the X had been presented in the posttarget letter stream. - In the experimental condition, a blank interval of 0, 90, 180, and 270 ms is presented between the target and the posttarget letter stream. - The probe is presented at one of the +1, +2, +3, +4, or +7 posttarget positions. **Results:** - **Probe detection**: The results demonstrate that this suppression mechanism is not ballistic in the specific way that was tested. - There is strong evidence that the posttarget processing deficit is sensitive to posttarget stimulation and that the suppression mechanism is initiated only when posttarget stimuli interfere with target identification. ### Experiment 4 This experiment tests whether a single posttarget item is enough to elicit the attentional suppression. **The experiment includes one condition:** - Subjects are asked to identify a white target letter embedded in a stream of black letters and subsequently respond whether an X (probe) had been presented in the posttarget letter stream. - Blank intervals of 0, 90, and 180 ms are inserted between the +1 and +2 items rather than between the target and the +1 item as in Experiment 3. **Results:** - **Probe detection**: When a blank interval of at least 90 ms is inserted after the first posttarget ISI and before the first posttarget letter, no evidence of a posttarget processing deficit is obtained. - This suggests that an attentional suppressive mechanism is used only when posttarget stimulation interferes with target identification. - The results indicate that the posttarget processing deficit is not initiated by the presentation of the target per se, but rather by the presentation of a letter stimulus immediately after the target. ## General Discussion These results suggest that the posttarget processing deficit is not a simple time-dependent phenomenon. The suppressive mechanism is sensitive to the nature of posttarget stimulation and only occurs when posttarget stimuli interfere with target identification. - The suppression mechanism is initiated by the recognition of the target and the simultaneous presentation of a +1 item (which interferes with target identification) before the target identification process is complete. - The mechanism may act ballistically, but it is not insensitive to posttarget stimulation. - The posttarget processing deficit may be relieved by the presentation of a blank interval between the target and the +1 item. This research contributes to the understanding of the attentional blink, a phenomenon that has been observed in a number of studies. 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