Brain Dynamics Underlying the Nonlinear Threshold for Access to Consciousness

When a flashed stimulus is followed by a backward mask, subjects fail to perceive it unless the target-mask interval exceeds a threshold duration of about 50 ms. Models of conscious access postulate that this threshold is associated with the time needed to establish sustained activity in recurrent cortical loops, but the brain areas involved and their timing remain debated. We used high-density recordings of event-related potentials (ERPs) and cortical source reconstruction to assess the time course of human brain activity evoked by masked stimuli and to determine neural events during which brain activity correlates with conscious reports. Target-mask stimulus onset asynchrony (SOA) was varied in small steps, allowing us to ask which ERP events show the characteristic nonlinear dependence with SOA seen in subjective and objective reports. The results separate distinct stages in mask-target interactions, indicating that a considerable amount of subliminal processing can occur early on in the occipito-temporal pathway (<250 ms) and pointing to a late (>270 ms) and highly distributed fronto-parieto-temporal activation as a correlate of conscious reportability

The role of phonology in visual word recognition: evidence from Chinese

Posters - Letter/Word Processing V: abstract no. 5024The hypothesis of bidirectional coupling of orthography and phonology predicts that phonology plays a role in visual word recognition, as observed in the effects of feedforward and feedback spelling to sound consistency on lexical decision. However, because orthography and phonology are closely related in alphabetic languages (homophones in alphabetic languages are usually orthographically similar), it is difficult to exclude an influence of orthography on phonological effects in visual word recognition. Chinese languages contain many written homophones that are orthographically dissimilar, allowing a test of the claim that phonological effects can be independent of orthographic similarity. We report a study of visual word recognition in Chinese based on a mega-analysis of lexical decision performance with 500 characters. The results from multiple regression analyses, after controlling for orthographic frequency, stroke number, and radical frequency, showed main effects of feedforward and feedback consistency, as well as interactions between these variables and phonological frequency and number of homophones. Implications of these results for resonance models of visual word recognition are discussed.postprin

Interactive effects of orthography and semantics in Chinese picture naming

Posters - Language Production/Writing: abstract no. 4035Picture-naming performance in English and Dutch is enhanced by presentation of a word that is similar in form to the picture name. However, it is unclear whether facilitation has an orthographic or a phonological locus. We investigated the loci of the facilitation effect in Cantonese Chinese speakers by manipulating—at three SOAs (2100, 0, and 1100 msec)—semantic, orthographic, and phonological similarity. We identified an effect of orthographic facilitation that was independent of and larger than phonological facilitation across all SOAs. Semantic interference was also found at SOAs of 2100 and 0 msec. Critically, an interaction of semantics and orthography was observed at an SOA of 1100 msec. This interaction suggests that independent effects of orthographic facilitation on picture naming are located either at the level of semantic processing or at the lemma level and are not due to the activation of picture name segments at the level of phonological retrieval.postprin

Cognitive Neuroscience Analyses of Memory: A Historical Perspective

As part of the general trend toward interdisciplinary research in recent years, a growing number of investigators have come to consider both cognitive and neuroscientific perspectives when theorizing about memory. Although such cognitive neuroscience analyses are a relatively recent development, the approach has precedents in earlier scientific thinking about memory. In this article we present a historical review of three major issues in memory research---consolidation processes, the nature of memory representations, and multiple memory systems. We discuss the nature of the relation between cognitive and neuroscientific approaches to each of these issues with respect to the distinction between collateral, complementary, and convergent relations (Schacter, 1986). Although some early investigators offered analyses that linked psychological and physiological perspectives, there is little historical evidence of systematic or sustained interdisciplinary research. However, more recent work, especially with respect to hypotheses about memory systems, suggests progress toward establishing programmatic interdisciplinary research.Psycholog

Passive frame theory: A new synthesis.

Passive frame theory attempts to illuminate what consciousness is, in mechanistic and functional terms; it does not address the “implementation” level of analysis (how neurons instantiate conscious states), an enigma for various disciplines. However, in response to the commentaries, we discuss how our framework provides clues regarding this enigma. In the framework, consciousness is passive albeit essential. Without consciousness, there would not be adaptive skeletomotor action

Ongoing Spontaneous Activity Controls Access to Consciousness: A Neuronal Model for Inattentional Blindness

Even in the absence of sensory inputs, cortical and thalamic neurons can show structured patterns of ongoing spontaneous activity, whose origins and functional significance are not well understood. We use computer simulations to explore the conditions under which spontaneous activity emerges from a simplified model of multiple interconnected thalamocortical columns linked by long-range, top-down excitatory axons, and to examine its interactions with stimulus-induced activation. Simulations help characterize two main states of activity. First, spontaneous gamma-band oscillations emerge at a precise threshold controlled by ascending neuromodulator systems. Second, within a spontaneously active network, we observe the sudden “ignition” of one out of many possible coherent states of high-level activity amidst cortical neurons with long-distance projections. During such an ignited state, spontaneous activity can block external sensory processing. We relate those properties to experimental observations on the neural bases of endogenous states of consciousness, and particularly the blocking of access to consciousness that occurs in the psychophysical phenomenon of “inattentional blindness,” in which normal subjects intensely engaged in mental activity fail to notice salient but irrelevant sensory stimuli. Although highly simplified, the generic properties of a minimal network may help clarify some of the basic cerebral phenomena underlying the autonomy of consciousness

Non-Being and Memory: A Critique of Pure Difference in Derrida and Deleuze

The psychology philosophy split has restricted viable readings of today\u27s psychological research. My project (within the philosophy of psychology) is to provide these readings. Specifically, in this dissertation I analyze the data and the interpretations of a large number of contemporary memory research articles. I use these articles to support my claim that Immanuel Kant misunderstood what in the Critique of Pure Reason he labeled affinity. Further, Jacques Derrida and Gilles Deleuze inherit this Kantian misunderstanding by way of G.W.F. Hegel\u27s attempt to eliminate it. Put another way, the component in question is that which grounds the post-structuralist justification for pure difference, and the wider context of this discussion is Plato\u27s problem of non-being. That is, Kant\u27s reading of affinity and Derrida\u27s and Deleuze\u27s respective readings of pure difference all function as failed attempts to solve the problem of non-being. Taking Plato\u27s Parmenides and Sophist as points of departure, I show how each of the above mentioned thinkers, including Aristotle, fails to meet Plato\u27s criteria for, i.e. solve, the problem of non-being. I then use contemporary memory research for the sake of enunciating my own solution to Plato\u27s problem. The critical structure of my discourse is directed at Derrida and Deleuze, then, as a critique of their readings of pure difference, and this is to accentuate the difference between my response to the problem and theirs. Kant\u27s misunderstanding of memory committed him to an ontological filled-duration illusion. On the one hand, my reading of contemporary memory research depicts being as bound by memory. On the other hand, memory\u27s binding is governed by play, i.e. memory as being\u27s play-ground. And, gaps can be noticed by regarding shifting engagements of procedural memory or memory\u27s cycling, though these gaps are often covered over by priming and habitual scripts. Hence, just as these gaps justify calling ontological filled-duration illusory, these gaps also constitute my solution to the problem of non-being. I paraphrase the fruit of solving the problem: Your being is not persisting; it is pulsing. Perhaps the largest impact of my solution is to be found in ethics