David J. Turk

A Positron Emission Tomography (PET) Study of Autobiographical Memory Retrieval

Memory for the experiences of ones life, autobiographical memory (AM), is one of the most human types of memory, yet comparatively little is known of its neurobiology. A positron emission tomography (PET) study of AM retrieval revealed that the left frontal cortex was significantly active during retrieval (compared to memory control tasks), together with activation in the inferior temporal and occipital lobes in the left hemisphere. We propose that this left frontal lobe activation reflects the operation of control processes that modulate the construction of AMs in posterior neocortical networks.

Mike or me? Self-recognition in a split-brain patient.

A split-brain patient (epileptic individual whose corpus callosum had been severed to minimize the spread of seizure activity) was asked to recognize morphed facial stimuli—presented separately to each hemisphere—as either himself or a familiar other. Both hemispheres were capable of face recognition, but the left hemisphere showed a recognition bias for self and the right hemisphere a bias for familiar others. These findings suggest a possible dissociation between self-recognition and more generalized face processing within the human brain.

Is the word length effect in STM entirely attributable to output delay?:evidence from serial recognition

Although it is generally accepted that the word length effect in short-term memory operates through output delay or interference, there is less agreement on whether it also influences performance through its impact on rehearsal. We investigated this issue by studying the effect of word length on recall and on a recognition task in which output delay was controlled. Word sequences were repeated exactly, or with one pair of words reversed. Two experiments using auditory presentation showed clear word length effects for both recall and serial recognition, although the magnitude of the effect tended to be less for recognition. A third experiment using visual presentation studied the effect of articulatory suppression during the recognition test; again we found a clear word length effect. It is concluded that the word length effect can influence retention through both rehearsal and output factors, as proposed by the phonological loop hypothesis.

Modulation of neural activity by angle of rotation during imagined spatial transformations

Imagined spatial transformations of objects (e.g., mental rotation) and the self (e.g., perspective taking) are psychologically dissociable. In mental rotation, the viewer transforms the location or orientation of an object relative to stable egocentric and environmental reference frames. In imagined shifts of perspective, the viewers egocentric reference frame is transformed with respect to stable objects and environment. Using fMRI, we showed that during mental transformations of objects the right superior parietal cortex exhibited a positive linear relationship between hemodynamic response and degrees of rotation. By contrast, during imagined transformations of the self, the same regions exhibited a negative linear trend. We interpret this finding in terms of the role of parietal cortex in coding the locations of objects in relation to the body.

Out of Contact, Out of Mind

Abstract: A truly remarkable aspect of human existence is the unitary sense of self that exists across time and place. Understanding the nature of self—what it is and what it does—has challenged scholars since antiquity. How can empirical research measure what it is to have a sense of self? We propose that the sense of self may emerge from the functions of a left hemisphere “interpreter” ( Gazzaniga, 2000 ). First, we examine evidence for the existence of self‐processing mechanisms in the intact brain, from behavioral and functional neuroimaging research. The available evidence suggests that the sense of self is widely distributed throughout the brain. Second, we discuss these findings in relation to what is known about higher cognitive functions in humans who have undergone a surgical procedure to sever the connection between the two cerebral hemispheres. Split‐brain research has facilitated an understanding of the way in which each cerebral hemisphere independently processes information. Research in this area has shown that each cerebral hemisphere features distinct information‐processing capabilities. This cognitive asymmetry is reflected in the notion of a left hemisphere interpreter module which, we have argued, generates a unitary sense of consciousness even in the disconnected brain. This chapter describes how this interpreter may also give rise to a unified sense of self.

When it becomes mine: Attentional biases triggered by object ownership

Previous research has demonstrated that higher-order cognitive processes associated with the allocation of selective attention are engaged when highly familiar self-relevant items are encountered, such as ones name, face, personal possessions and the like. The goal of our study was to determine whether these effects on attentional processing are triggered on-line at the moment self-relevance is established. In a pair of experiments, we recorded ERPs as participants viewed common objects (e.g., apple, socks, and ketchup) in the context of an “ownership” paradigm, where the presentation of each object was followed by a cue indicating whether the object nominally belonged either to the participant (a “self” cue) or the experimenter (an “other” cue). In Experiment 1, we found that “self” ownership cues were associated with increased attentional processing, as measured via the P300 component. In Experiment 2, we replicated this effect while demonstrating that at a visual–perceptual level, spatial attention became more narrowly focused on objects owned by self, as measured via the lateral occipital P1 ERP component. Taken together, our findings indicate that self-relevant attention effects are triggered by the act of taking ownership of objects associated with both perceptual and postperceptual processing in cortex.

Mine to remember: The impact of ownership on recollective experience

Evaluating information with reference to self is associated with enhanced memory, the “self-reference effect”. The effect is found in recognition accompanied by recollective experience (remembering), but not in recognition based on a feeling of knowing. The current research employed an ownership procedure to investigate whether less evaluative forms of self-referential cognition produce similar enhancement of recollective experience. Participants were asked to sort items into baskets that belonged to themselves or a fictitious other. A subsequent remember–know recognition test showed that items encoded in the context of self-ownership were more likely to be correctly recognized than other-owned items. This ownership effect was found in remember, but not know, responses. This finding suggests that creating a self-referential encoding context leads to elaborative representations in episodic memory, even in the absence of explicit self-evaluation.

Mine and me: Exploring the neural basis of object ownership

Previous research has shown that encoding information in the context of self-evaluation leads to memory enhancement, supported by activation in ventromedial pFC. Recent evidence suggests that similar self-memory advantages can be obtained under nonevaluative encoding conditions, such as when object ownership is used to evoke self-reference. Using fMRI, the current study explored the neural correlates of object ownership. During scanning, participants sorted everyday objects into self-owned or other-owned categories. Replicating previous research, a significant self-memory advantage for the objects was observed (i.e., self-owned > other-owned). In addition, encoding self-owned items was associated with unique activation in posterior dorsomedial pFC (dMPFC), left insula, and bilateral supramarginal gyri (SMG). Subsequent analysis showed that activation in a subset of these regions (dMPFC and left SMG) correlated with the magnitude of the self-memory advantage. Analysis of the time-to-peak data suggested a temporal model for processing ownership in which initial activation of dMPFC spreads to SMG and insula. These results indicate that a self-memory advantage can be elicited by object ownership and that this effect is underpinned by activity in a neural network that supports attentional, reward, and motor processing.

From facial cue to dinner for two: the neural substrates of personal choice

The current experiment examined the neural substrates of response selection, comparing conditions that required participants to make criterion-free selections from sets of same-sex faces (i.e., inconsequential decision) to choosing a dinner date from opposite-sex faces (i.e., consequential decision). In each of these tasks, either a single face (i.e., no choice) or two or three faces (i.e., free choice) appeared for selection. The results revealed that regions of dorsal premotor cortex (PMd) and parietal cortex bilaterally, as well as an area along the medial surface of the superior frontal gyrus, were activated by both consequential and inconsequential decisions, thereby providing evidence for a common selection network. Consequential decisions were further indexed by activation of the insula/ventrolateral prefrontal cortex (BA 47) and the paracingulate gyrus (BA 32). The implications of these findings for current accounts of response selection and social-cognitive functioning are considered.

SELF: FROM SOUL TO BRAIN

Abstract: A truly remarkable aspect of human existence is the unitary sense of self that exists across time and place. Understanding the nature of self—what it is and what it does—has challenged scholars since antiquity. How can empirical research measure what it is to have a sense of self? We propose that the sense of self may emerge from the functions of a left hemisphere “interpreter” ( Gazzaniga, 2000 ). First, we examine evidence for the existence of self‐processing mechanisms in the intact brain, from behavioral and functional neuroimaging research. The available evidence suggests that the sense of self is widely distributed throughout the brain. Second, we discuss these findings in relation to what is known about higher cognitive functions in humans who have undergone a surgical procedure to sever the connection between the two cerebral hemispheres. Split‐brain research has facilitated an understanding of the way in which each cerebral hemisphere independently processes information. Research in this area has shown that each cerebral hemisphere features distinct information‐processing capabilities. This cognitive asymmetry is reflected in the notion of a left hemisphere interpreter module which, we have argued, generates a unitary sense of consciousness even in the disconnected brain. This chapter describes how this interpreter may also give rise to a unified sense of self.