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Selective Attention: Effects of Perceptual Load on Visual Tasks of Attention EFFECTS OF PERCEPTUAL LOAD ON ATTENTION 1 Running head: WHAT ARE THE EFFECTS OF PERCEPTUAL LOAD ON VISUAL TASKS OF SELECTIVE ATTENTION? Selective Attention: Effects of perceptual load on visual tasks of attention Adaline Rasmijn Tilburg University, the Netherlands Developmental Psychology Department Masterthesis P & GG ANR: 381938 Begeleider: Dr. J.G.M. Scheirs Tweede beoordelaar: Dr. M.J.A. Feltzer Datum: 25-08-2014 EFFECTS OF PERCEPTUAL LOAD ON ATTENTION 2 Abstract In the present study, Lavie’s perceptual load theory was tested to settle a long-standing debate between early selection theories, implying that only the attended stimuli are processed because of limited capacity, and late selection theories, implying that all information is fully processed but only selected stimuli are given access to further processing stages such as memory. According to Lavie’s theory, it depends on perceptual load whether information is processed early or late. It was anticipated that during high perceptual load (difficult task), early selection would be the chosen strategy and during low perceptual load (easier task), the chosen strategy would be late selection. Participants consisted of 10 females and 10 males (age 18-23 years), who were undergraduate university students. Participants were tested individually using a computer- administered visual selection task with three levels of difficulty, defined by inter-stimulus interval (speed) and Target Type. Repeated measures MANOVA showed significant main effects of inter-stimulus interval and Target Type for all three assessment factors (reaction time, hit rate and false alarm rate). The hypothesis was confirmed, which supports Lavie’s theory that when a task is more difficult and there is only sufficient capacity to attend to relevant stimuli, early selection is used. However, when the task is easier and all information can be attended to, late selection is used. EFFECTS OF PERCEPTUAL LOAD ON ATTENTION 3 Selective Attention: effects of perceptual load on visual tasks of attention Attention is the cognitive process of selectively attending to particular and relevant aspects in the environment while ignoring other irrelevant aspects. A popular example is the cocktail party effect, listening to what someone is saying while ignoring other conversations in the room except when those conversations contain your own name (Cherry, 1953). The topic of attention is one of the most intensely studied in psychology. The reason for all this focus on attention is because attention is necessary for a variety of cognitive purposes, for example attention is needed for perception, memory and language. Another reason why it is important to do research on the mechanisms of attention is because attention deficits are found in neurological and psychiatric disorders, such as ADHD, autism spectrum disorders or schizophrenia. Accordingly, the studies of attention provide insight into clinical disorders. Another main goal of studying attention is to describe the factors of focused attention that allow people to ignore irrelevant distractions (Lavie, 2010). In the 1950’s, Broadbent’s filter theory was the first to describe the human’s processing system using an information processing metaphor (Fernandez-Duque & Johnson, 1999). In his theory, Broadbent (1958) proposed an early selection theory of attention, which states that humans process information with limited capacity and information to be processed is selected early. Due to our limited capacity, a selective filter is needed for information processing. According to Broadbent, all stimuli are initially processed for basic, physical properties, such as pitch, color, loudness and direction. Thus, the selective filter allows for certain stimuli to pass through the filter for further processing, while the unattended stimuli are filtered out and lost. Broadbent emphasized the splitting of incoming stimuli to attended or unattended channels. The selection of a channel is guided through attention. Information selected to pass through the filter is then available for short-term memory and for manipulation, prior to storage in long-term memory. If EFFECTS OF PERCEPTUAL LOAD ON ATTENTION 4 someone is actively attempting to attend to a stimulus based on his intentions (current goals), then voluntary attention or top-down processing will be employed. However, if a sensory event catches one’s attention, then reflexive attention or bottom-up processing will be employed (Lachter, Forster, & Ruthruff, 2004). Visual search experiments by Yantis and Jonides (1984) showed that when an item appears abruptly, it is always processed first. Broadbent’s filter theory then postulates that a selective filter is needed to cope with the overwhelming amount of information entering the channels, such that certain messages are filtered out or inhibited from the messages that were filtered for further processing. This filter theory reflects an early selection theory because only certain information is selected and attended to at an early stage of information processing (Broadbent, 1958). An important piece of evidence for Broadbent’s theory was acquired through a dichotic listening task. This task has been extensively used to test for attended and unattended information presented to a participant. During this task, participants were presented with different letters in each ear simultaneously and were asked to repeat in any order. What Broadbent (1958) found was that participants repeated what they heard in one ear followed by the other ear (ear-by-ear), instead of in order of presentation. This led him to conclude that we can only pay attention to one channel at a time. In short, early selection theories suggest that attention can prevent irrelevant stimuli from reaching awareness (Broadbent, 1958), more specifically a selective filter in the brain rejects the irrelevant stimuli before its content is fully analyzed (Treisman & Geffen, 1967). On the other hand, Deutsch and Deutsch (1963) were proponents of the late selection theory, which says that all stimuli are fully identified when perceived, but only the attended stimuli are given access to further stages, such as long-term memory and motor control. In other EFFECTS OF PERCEPTUAL LOAD ON ATTENTION 5 words, both believed there was a type of ‘central bottleneck’ and a selection device prior to it. Their disagreement regarded the location of the selection device; did the selection occur before after perceptual awareness? According to Deutsch and Deutsch the selection occurred after physical and semantic analysis of the stimuli, while according to Broadbent the selection occurred before semantically analyzing the stimuli but after physical analysis of the stimuli (as shown in Figure 1). Figure 1. A comparison between early (A) and late selection (B) theories. S stands for stimulus. According to early selection the stimuli are analyzed only on their physical properties before they are perceived into awareness and require a response. On the other hand, according to late selection the stimuli are analyzed both on their physical and semantic properties before they are perceived into awareness and require a response. What Deutsch and Deutsch (1963) found during the dichotic listening task was that both channels are recognized but are quickly forgotten unless they have personal significance to the participant, such as his or her own name. In short, late selection theories suggest that all stimuli are fully analyzed and attention only affects later processes such as response selection and memory but does not affect perceptual awareness (Deutsch & Deutsch, 1963). EFFECTS OF PERCEPTUAL LOAD ON ATTENTION 6 There was substantial evidence that supported both the early selection and the late selection theory. Studies of attention that used the dichotic listening task (Treisman & Geffen, 1967) and the selective-looking task (Becklen & Cervone, 1983) demonstrated that unattended information typically goes unnoticed, which supports the early selection theory (Lavie et al., 2004). Becklen and Cervone (1983) explain that in a selective-looking task subjects are presented with two videotaped or filmed naturalistic episodes simultaneously, printed above one another, and are asked to attend selectively to one and to ignore the other. However, the late selection theory received support in later studies that used indirect measures of distractor perception in Stroop- like tasks (Eriksen & Eriksen, 1974). In a Stroop task subjects are asked to name the ink color of written color words (e.g., say blue to the word green written in blue ink). A compromise between these two theories seemed nearly impossible. However, the load theory by Lavie resolves the early and late selection debate by the hypothesis that perceptual processing has limited capacity but proceeds automatically in an involuntary, mandatory manner on all information within its capacity (Lavie, 2005). In other words, the perceptual load theory incorporates both aspects of the early and late selection theories by stating that perceptual capacity is limited (early selection) and that all stimuli are processed automatically (late selection) until capacity runs out. Among Lavie’s main findings is that high perceptual load engages full capacity in relevant processing and hereby reduces irrelevant distractor perception (Lavie, 2010), which means that the relevant stimuli are selected early on in the process. In contrast, in situations of low perceptual load, spare capacity remaining beyond the task-relevant processing
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