Visual Attention and Consciousness

Jay Friedenberg

• Publisher: Psychology Press
• Year: 2012
• eBook ISBN: 9781135105501
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

Consciousness is perhaps one of the greatest mysteries in the universe. This ambitious book begins with a philosophical approach to consciousness, examining some key questions such as what is meant by the term "conscious," and how this applies to vision.

The book then explores major visual phenomena related to attention and conscious experience—including filling-in processes, aftereffects, multi-stability, forms of divided attention, models of visual attention, priming effects, types of attentional blindness and various visual disorders. For each phenomenon, the biological and cognitive level research is reviewed. Themes touched upon throughout are the relation between consciousness and attention, automatic vs. willful processes, singularity vs. multiplicity, and looking without seeing. The book concludes with an evolutionary approach, describing possible functions that visual consciousness may serve and how those may affect the way we see.

The systematic review of key topics and the multitude of perspectives make this book an ideal primary or ancillary text for graduate courses in perception, vision, consciousness, or philosophy of mind.

1

Introduction

THEMES AND CHAPTER ORGANIZATION

We cover a lot of ground in this book, surveying the empirical literature on many different aspects of visual attention and consciousness. In order to organize all this information and show how it is inter-related we divide the subject up into seven main themes. We devote one or two chapters to developing each of these themes, a preview of which is given below. Each chapter section that describes a unique perceptual phenomenon begins with an everyday example followed by a definition. We then discuss the perceptual, cognitive, and neuroscience research on the topic and how it relates to visual attention and consciousness.

THEME 1: CONSCIOUSNESS AND ATTENTION

We start by introducing the concept of consciousness. There are many different types of conscious experience so we briefly present different proposed categorization schemes. Our focus will be entirely on perceptual consciousness, specifically visual conscious experience. We then introduce attention and describe how it differs from consciousness. Attention and consciousness are closely related but recent work shows that they are not the same. It is possible to be conscious of something while not paying attention to it and to pay attention to something while not being conscious of it. Following this we present several classic thought experiments on consciousness and frame the major philosophical issues. The scientific approach to studying this phenomenon advocates a monist materialist stance that should attempt to bridge the explanatory gap between objective and subjective measures of awareness. Consciousness is best studied using both older reductionist and newer emergent approaches.

Because much of what we will discuss centers on underlying brain areas, we will introduce some of the anatomical and physiological underpinnings of vision before getting into a detailed description of the literature. The brain areas underlying conscious and unconscious vision are discussed along with the idea of the neuronal correlates of consciousness and the theory of neural synchrony. We then sketch out the structural and functional basis of visual attention along with biological models and some of the problems encountered in doing this type of research. In Chapter 7 we present different varieties of attention including preattentive and attentive, exogenous and endogenous, and object- and space-based forms.

THEME 2: AUTOMATIC MECHANISMS

Our visual world is actively constructed and a lot of what we experience is the result of lower level automatic processes. We aren’t aware of our blind spot even though there are no photoreceptors in this part of the retina to provide information about what is located there. We don’t notice the world “jumping” whenever we make an eye movement because of saccadic suppression. The visual system fills in this region so that we aren’t even aware that we are missing anything. There are also more complex types of filling in that occur. In perceptual completion, we build up the hidden parts of objects that are occluded so that they seem complete even though we glimpse only a part of them.

It is easy to fatigue the visual system if we look at something for too long. Under these conditions we often experience aftereffects. We examine three different types of aftereffects for color, motion, and tilt in which we seem to “bounce back” and be aware of stimuli that are the opposite of what we’ve been staring at. These experiments demonstrate that opponency and mutual inhibition are an important part of how we see. Another instance of opposing effects in perception comes from binocular rivalry, figure ground, and ambiguous figures. In these cases the stimulus remains constant but we alternate back and forth between two different perceptions, each fighting to dominate our awareness.

THEME 3: SINGULARITY AND MULTIPLICITY

Is consciousness a single thing or are there many different streams of it? This question has occupied philosophers for millennia. Only in recent years has science been able to give us a better answer. It is possible to focus on a single thing at a time. This is known as selective attention. We survey the many models of selective attention that have been proposed to explain how it is we choose to have one thing enter awareness. We then contrast this with what is also true: our ability to split or divide our attention such that we can take in many different things at once.

Anatomically our visual system channels information into two separate pathways. One is the dorsal stream that feeds into the parietal lobes. This “where” stream allows us to identify the location of objects and how we should act toward them. The other is the ventral stream that feeds into the temporal lobe. This “what” stream enables us to identify and recognize objects. The two cerebral hemispheres are another major anatomical division of labor. Although it is a simplification, our left hemisphere is specialized in most people for linguistic skill while the right tends to favor spatial skills. Each hemisphere appears to have its own distinct consciousness. In split-brain patients, the two hemispheres can fight for control of awareness.

THEME 4: FORCED SEEING

In this section we first examine the case where we can’t miss seeing something: where stimuli grab our attention and force themselves into our conscious awareness even if we don’t want them to. In one condition of the Stroop effect it is impossible to state the color of a word while ignoring its name. One explanation for this is that reading is such a well-practiced skill that the visual system automatically processes a word’s meaning. Similarly, in the flanker task we are asked to identify a central letter or stimulus while ignoring distractors that lie on either side. Even when focused on the target, we can’t help but process these distractors, suggesting that whatever falls inside a “window” of attention is processed automatically.

Saliency maps are a convenient way of representing where in the visual field our attention goes. Luminance, color, and orientation changes have all been proposed as regions that will capture attention and that have been incorporated into computational models to predict eye movements. In attention orienting, stimuli cause us to orient our eyes and head toward some stimulus of significance. Examples include moving objects, emotional faces, and gaze direction.

THEME 5: LOOKING WITHOUT SEEING

Next we examine cases where you can be looking at something but not see it. In priming and masking experiments researchers present a stimulus such as a word very quickly. Observers report no conscious awareness of having seen the word but it influences their behavior nonetheless, indicating that it has been processed at an unconscious level. In the attentional blink and repetition blindness phenomena we miss a second target because we are still busy processing a target that came before it. In change blindness we miss seeing even obvious changes to two scenes when they are alternated. Inattentional blindness occurs when we fail to see an object or event when we are staring right at it, demonstrating that attention is not always centered at the point of fixation.

THEME 6: DAMAGED BRAINS

Apart from measuring intact brains, there is also much to be gained by looking at deficits incurred as the result of brain damage. There are a large number of different visual disorders, each with very modality-specific effects. In Chapter 11 we cover the large number of different object processing disorders, known as visual agnosias. We look at case studies, symptoms, and explanations for different agnosias that include difficulties perceiving color, motion, objects, faces, and even a deficit in realizing one has a deficit. In Chapter 12 we summarize other fascinating consciousness deficits such as scotomas, blindsight, and problems in allocating attention correctly as is the case in neglect, extinction, and Balint’s syndrome.

THEME 7: EVOUTIONARY INFLUENCES

We end the the book by looking at evolutionary themes. Why is there a need for conscious vision? What role does attention play in the survival of the organism? There are various proposals for why such awareness is important. We will examine these and conclude with a very general theory of consciousness and how it may operate in the brain as dynamic pattern of activation. We compare the various models that have been proposed to account for conscious vision and make suggestions for how they may be integrated. The future of consciousness research is bright—increases in technology and new methods will undoubtedly bring us closer to understanding this phenomenon.

WHAT IS CONSCIOUSNESS?

Consciousness is perhaps one of the greatest mysteries in the universe. How is it that we are aware of ourselves? Why is it that we have minds? The universe seems as if it could just as easily exist without out any sort of consciousness. From a scientific standpoint the universe could work just as well without it. Many complex physical processes operate just fine without any type of awareness. Physics, chemistry, biology, and other sciences seem adequate to describe many natural phenomena such as the movement of tides, cell physiology, and plant life. So why can’t science provide us with a complete explanation of consciousness? We will examine these questions but first need to lay down some groundwork.

Obviously any starting point in the study of consciousness must begin with a definition. What is consciousness? The answer is not so easy. In fact, a recent book on the topic has been written without providing any definition (Blackmore, 2012). It might help then to start by describing what philosophers have said about it. Nagel (1974) provides us with an intriguing argument. He asks us to think about a bat using echolocation to navigate and pursue insects while flying around. The bat emits a pulse of sound. When the sound hits an object it bounces back an echo. The bat then analyzes the echo to determine the distance and other properties of the object. Nagel argues that “there is something that it is like” to be a bat using echolocation. Just as we hear a sound and interpret its meaning, the bat interprets its echoes in some sort of meaningful way. It seems reasonable to suppose that the bat has an experience or is aware of the sound. It is this experience or awareness that we wish to understand. However, because this understanding is derived from being a bat, we will never be able to share the experience.

Consciousness is a subjective experience. Although we may be able to better understand what it is like to be another human hearing a Beethoven symphony, smelling a rose or seeing a Monet painting, we can never be sure that we are actually having the exact same experience ourselves. In other words, consciousness is a subjective phenomenon. You and only you can know what it is like to hear a symphony. When it comes to studying consciousness scientifically this poses a big problem. Science is an objective endeavor. As such, it can only provide us with objective descriptions. It can tell us which neurons in the brain are active and at what times but it can’t explain what it is like to be the person whose brain is acting in that way. At best, science can provide a complete mapping of objective to subjective phenomena, it can tell us what is going on in the brain whenever we have an experience, but it can’t explain the subjective quality of experience, known as its qualia.

This objective/subjective difference is known as the explanatory gap. It seems as if there will always be a gap between what can be described objectively and what can be experienced subjectively, between having a brain and having a mind, and between our “inner” world and the “outer” world. This gap is what makes consciousness such a puzzle and has intrigued philosophers and scientists from the very beginning. Jackson (1982) poses this difference using a thought experiment. He asks us to think about a neuroscientist named Mary. Mary lives in the future and as a neuroscientist she understands everything there is to know about color vision. But Mary has been brought up in a black and white room and has viewed the world only through a black and white TV monitor. One day we take Mary out of her room and have her experience the world in full color for the first time. Will Mary be amazed at the color red or will she simply acknowledge that she always knew it would look this way? According to Jackson, Mary will learn something new. There will be some additional information generated by this experience that cannot be explained by science, the qualia, or subjective feel of seeing the color red.

Another way to think about consciousness is the “zombie” thought experiment. Imagine somebody who physically and behaviorally is indistinguishable from you. They walk, talk, carry on a conversation, and do everything the way you do. The only difference is that your zombie is unconscious (Moody, 1994). If such a zombie were possible, then we would have to admit that consciousness is not necessary. Some have suggested that it might even be optional, like getting leather seats when buying a new car. In this case, we would have to believe that consciousness makes no difference, and we can get along just fine without it. The question we would need to answer then is why we have consciousness at all and what purpose it serves. This issue is addressed in Chapter 13. On the other hand, if you determine that these sorts of zombies are not possible, then the question becomes how consciousness comes about in people like us.

VARIETIES OF CONSCIOUSNESS

Consciousness is difficult to understand in part because there are so many different types. There are broad categories of consciousness that differ from each other qualitatively. For instance, global brain activity varies dramatically when awake compared to when we are in different stages of sleep. There are also major differences between being conscious and unconscious. Physicians use a categorization scheme to describe levels of nonconscious states. A shallow form of consciousness is called a minimally conscious state, while a deeper comatose condition is a vegetative state, deeper than this and a patient is said to be in a coma. We must also consider the case where an individual can be under the influence of some drug such as marijuana or LSD and the way this state differs from being sober.

Many early psychologists had their own particular categories of conscious states. The psychoanalytic psychologist Sigmund Freud proposed the unconscious, preconscious, and conscious. William James differentiated between dynamic and static forms of thought that he labeled as transitive and substantive, respectfully (James, 1890). The philosopher Ned Block more recently has a four-fold classification of conscious states, two of which we will discuss here and two that we will discuss later (Block, 1995). He states that we have a monitoring consciousness, which is that part of our mind that can think about other parts of our mind. This “thinking about thinking” is also referred to as metacognition. We also seem to have a self-consciousness that is our awareness of our self as having a mind and a body that is separate from others and from the environment. The neuroscientist Antonio Damasio believes that our self-consciousness is formed from signals about our bodily states that are sent to our brain (Damasio, 2000).

Another classification scheme we can use is based on the source, type, and mode of consciousness (Table 1.1). If we are attending to stimuli in the environment as when we are looking at a palm tree, then the source of information is external. If we are forming a visual image of a palm tree with our eyes closed, then the informational source is internal. Type of consciousness can be considered as falling into three main categories: perception, cognition, and emotion. If we are attending to visual, auditory, olfactory, gustatory, or tactile inform...

Table of contents

• Front Cover
• Visual Attention and Consciousness
• Title Page
• Copyright
• Contents
• Acknowledgements
• Chapter 1 Introduction
• Chapter 2 Neural Underpinnings
• Chapter 3 Under Construction
• Chapter 4 I’m Getting Tired of This
• Chapter 5 Same but Different
• Chapter 6 One or Many?
• Chapter 7 Varieties of Visual Attention
• Chapter 8 Your Attention Please
• Chapter 9 Now You See It, Now You Don’t
• Chapter 10 Looking without Seeing
• Chapter 11 The Damaged Brain: Agnosias
• Chapter 12 The Damaged Brain: Other Disorders
• Chapter 13 Conclusion
• References
• Index