Is Visual Stimuli Neighboring Attended Stimuli Suppressed in High Perceptual Load ?

3 INTRODUCTION . 6 BACKGROUND . 6 THE CURRENT STUDY . 10 ALTERNATIVE THEORIES . 11 LIMITATIONS OF THE STUDY . 12 METHOD.12 SUBJECTS . 12 STIMULI . 12 PROCEDURE . 13 DESIGN . 14 EEG RECORDINGS AND ANALYSIS . 14 STEADY STATE VISUAL EVOKED POTENTIALS (SSVEPS) . 15 EVENT RELATED POTENTIALS (ERPS) . 16 RESULTS . 16 BEHAVIOURAL PERFORMANCE . 16 SSVEPS . 17 ERPS . 18 DISCUSSION.19 RESULT DISCUSSION . 20 Assuming there is no Effect of Load in the Data . 21 Assuming there is an Effect of Load in the Data . 21 METHOD DISCUSSION . 22 CONCLUSION . 23 REFERENCES . 24 Is Visual Stimuli Neighboring Attended Stimuli Suppressed in High Perceptual Load? 6 Introduction This study aims to add evidence and understanding in the neuropsychological attempt to figure out how human perception works. More specifically, how we perceive our environment and how we focus our attention to be able to make sense of the world and not be overwhelmed by the multitude of stimuli surrounding us. In the past and still today, the neural and cognitive mechanisms that allow our perception are debated and many theories have been suggested, some of which will be discussed below. Perception and attention are cognitive functions that are important in our everyday life to be able to function in the world around us, act and interact appropriately with other people and things in our environment. A better understanding of our attentional and perceptual system could help improve design in situations where human attention and perception plays a vital roll, for example in driving situation. Understanding the relationship between attention and perception could also be an important contributor to reversing attentional deficit disorders. Background The environment is filled with stimuli. Our sensory systems are dedicated to register and process information from the world and make us conscious of our environment. Our awareness of our environment is in cognitive terms called perception and defined by Purves et al. (2008, pp. 40-41) as: “. the conscious awareness of external and internal environment generated by neural processing carried out by the human sensory systems . In vision, the fundamental qualities of perceptual awareness are brightness, color, form, depth and motion . [The] complex aspects of conscious awareness quickly transcend the notion of perception as simply the end result of sensory processing and clearly depend on a host of other cognitive functions including learning, memory, emotional reactions and social context. Thus what we perceive is, in the end, determined by far more than sensory input. ” These cognitive functions in perception are what make our environment comprehensible to us by giving a meaning to the perceived stimuli. It prevents us from being overwhelmed by the multitude of stimuli constantly present in our everyday lives by focusing on relevant stimuli. A traditional way of understanding the processing of stimuli is through the division of bottom-up (Purves, et al., 2008) (Sternberg, 2009, pp. 102-114) and top-down (Purves, et al., 2008) (Sternberg, 2009, pp. 102-114) processing. Top-down processing is the brains way of using knowledge stored in memory for predicting possible outcomes occurring in our environment by anticipating a meaning of the stimuli before it occurs in our environment. Bottom-up processing on the other hand, suggests that stimuli are sequentially processed from low to high processing Is Visual Stimuli Neighboring Attended Stimuli Suppressed in High Perceptual Load? 7 levels: the meaning of the stimuli (i.e. high level of processing) is given after the stimuli being decoded (i.e. low level of processing). Most probably, both bottomup and top-down processed are used to most efficiently and most accurately make sense of the world around us (Purves et. al, 2008) (Sternberg, 2009). As a function of our interests, motivations and goals, only small portions of stimuli in our environment are relevant. It is then important to be able to select relevant stimuli and ignore irrelevant stimuli to not be overwhelmed by all the inputs. This selection process is a phenomenon referred to as selective attention (Purves, et al., 2008) (Sternberg, 2009). A common example of selective attention is the cocktail party effect (Cherry, 1959), which refers to the fact that despite not attending the conversations surrounding the one you are focusing on, you are still able to react to relevant stimuli (such as your name) if it is mentioned in the background noise. Selective attention is not restricted to auditory stimulation, but is shown to also be present for visual stimulation (Purves, et al., 2008) (Sternberg, 2009). Phenomenon such as change blindness (Rensink, O'Regan, & Clark, 1997) (dothetest, 2008) (i.e. when something in the visual field is changed without you noticing) or inattentional blindness (Simons & Chabris, 1999) (Simons & Chabris, 2013) (i.e. when a visual stimuli is entirely missed) provide evidence that some visual information is filtered out and does not reach consciousness. The debated question is whether this filtering process occurs at an early or late stage in perceptual processing. Neural processing is faster for attended than unattended stimuli suggesting an attentional spotlight (Purves, et al., 2008). The attentional spotlight demonstrates the ability to focus visual attention on a particular spatial location within the visual field (not necessarily at eye fixation) and thereby process the attended stimuli (i.e. the stimuli covered by the attentional spotlight) faster and more efficiently than remaining stimuli in the visual field (Posner, 1980). Selective attention suggests a neural function that selects relevant stimuli for further processing and finally resulting in conscious visual experience or sensation. Several theories exist about how and when in visual sensory processing this selection occurs. For example early selection theory (Purves, et al., 2008, pp. 4344) (Sternberg, 2009, pp. 153-157) suggests that stimuli is filtered out early in processing and not object to further processing. Conversely, the late selection theory (Purves, et al., 2008, pp. 43-44) (Sternberg, 2009, pp. 153-157) suggests that all stimuli are processed at an early and low level and the filtering mechanism is present at later and higher levels of processing. In an attempt to settle the debate between early and late selection theories, Lavie (1995) presented findings forming a foundation for a theory that merges these two alternatives: the perceptual load theory. Perceptual load is explained to be higher if more features are required to be distinguished in order to correctly Is Visual Stimuli Neighboring Attended Stimuli Suppressed in High Perceptual Load? 8 identify an object (Treisman & Gelade, 1980). If