Global model analysis by parameter space partitioning

To model behavior, scientists need to know how models behave. This means learning what other behaviors a model can produce besides the one generated by participants in an experiment. This is a difficult problem because of the complexity of psychological models (e.g., their many parameters) and because the behavioral precision of models (e.g., interval-scale performance) often mismatches their testable precision in experiments, where qualitative, ordinal predictions are the norm. Parameter space partitioning is a solution that evaluates model performance at a qualitative level. There exists a partition on the model's parameter space that divides it into regions that correspond to each data pattern. Three application examples demonstrate its potential and versatility for studying the global behavior of psychological models.     

Effects of nicotine deprivation on craving response covariation in smokers

Most models of craving propose that when cravings are strong, diverse responses--thought to index an underlying craving state--covary. Previous studies provided weak support for this hypothesis. The authors tested whether nicotine deprivation affects degree of covariation across multiple measures related to craving. Heavy and light smokers (N = 127) were exposed to smoking cues while either nicotine deprived or nondeprived. Measures included urge ratings, affective valence, a behavioral choice task assessing perceived reinforcement value of smoking, and smoking-related judgment tasks. Results indicated higher correlations in the nicotine-deprived than in nondeprived group. The measures principally responsible for this effect loaded onto a single common Craving factor for nicotine-deprived but not nondeprived smokers. These findings suggest that, under certain conditions, measures of craving-related processes covary.     

Inhibition of return and manual pointing movements

To examine whether the motor inhibition of return (IOR) postulated by Taylor and Klein (1998, 2000) generalizes to manual guided movements or is restricted to saccadic responses, the following three experiments were conducted. The first experiment combined peripheral cues (which generate IOR) with four types of manual responses made to central targets (central arrow indicating the response location). The responses were made on a touch-screen and were the equivalent of either a detection keypress, a choice keypress, a detection-guided pointing movement, or a choice-guided pointing movement. No IOR was found for any of the responses. The second experiment replicated the main result under eye fixation control. In Experiment 3, peripheral cues and peripheral targets were used, and IOR was present in all responses. Overall, these finding suggest that motor-based IOR is restricted to the oculomotor system. Implications for motor-based IOR and attention-based IOR are discussed.     

Demythologizing the emotions: adaptation,cognition, and visceral representations of emotion in the nervous system

This article highlights four issues about the neurobiology of emotions: adaptation vs. dysfunction, peripheral and central representations of emotion, the regulation of the internal milieu, and whether emotions are cognitive. It is argued that the emotions evolved to play diverse adaptive roles and are biologically vital sources of information processing. They were not designed as pieces of pathology, though they certainly can underlie some psychophathologies. Emotions are, in part, appraisal systems that are operative at numerous level of the nervous system from the brainstem to the cortex. Like other information processing systems they are not perfect cognitive systems. Emotional systems often utilize somatic and visceral information for appraisals of events to facilitate decisions of whether to approach or avoid objects. The neural systems of emotions traverse the entire neural axis and are linked to the regulation of the internal milieu. Thus, in addition to the experiential aspects of emotions, emotions embody appraisal systems that are pervasive to all levels of the brain to facilitate function, adaptation, and survival.     

Inhibition of return spreads across 3-D space

Focusing attention to a location in 3–D space operates much the same as in 2–D space. Attending a location in 2–D space is followed by a selective inhibitory aftereffect known as inhibition of return (IOR). Here, we report the results of two 3–D reflexive cuing studies in which depth was defined by binocular disparity. As has been shown before, attentional cuing was specific for x–y–z locations. However, the present results show that IOR is not depth specific. After a specific location in x–y–z is cued, IOR occurs for the depth plane in front of and behind the cued location. The finding that IOR spreads across depth planes may be related to how inhibited locations are encoded in the superior colliculus. We argue that the functional role of a depth–blind IOR is to bias attention against going back to any part of a previously attended object.     

A Descriptive Study of Pain and Quality of Life following Guillain-Barré Syndrome: One Year Later

Guillain-Barré syndrome (GBS) is a debilitating immunopathy that afflicts approximately 5,000 patients annually in the United States, a number that represents roughly half of the incidence of spinal cord injuries (J. M., Meythaler, 1997). Of these 5,000 new cases per year, 4–15% will die, 20% will possess deficits in ambulation or require ventilator assistance more than one year later, and more than two-thirds will have persistent fatigue (J. M., Meythaler, 1997; Hughes et al., 2003). These figures suggest that GBS is currently a legitimate cause of long-term disability.Many secondary complications may follow GBS that include dysautonomia, deep vein thrombosis, anemia, immobilization, and pain and sensory involvement (J. M., Meythaler, 1997; J. M. Meythaler, M. J. De Vivo, and W. C. Braswell, 1997). These medical complications have not been studied systematically, and the psychosocial complication of pain following GBS has certainly been overlooked in the literature. The present paper utilized a limited sample of 18 patients (N = 18) with persistent motor deficits at least one year after onset of GBS. We examined their pain and perceived quality of life as part of an ongoing federally funded study which will ultimately attempt to determine if 4-aminopyridine (4-AP) significantly improves motor function in patients with residual weakness from GBS. Findings suggest that while most persons do not rate themselves as depressed one year after GBS onset, 22% of respondents did exceed the cutoff for clinical depression on the CES-D. Age and gender do not appear to be related to any component of pain in GBS; however, self-ratings of physical and mental health do appear to be significantly related to pain experience. The nature of this relationship was not determined, and merits further investigation in future studies.     

Posterior parietal cortex activity predicts individual differences in visual short-term memory capacity

Humans show a severe capacity limit in the number of objects they can store in visual short-term memory (VSTM). We recently demonstrated with functional magnetic resonance imaging that VSTM storage capacity estimated in averaged group data correlated strongly with posterior parietal/superior occipital cortex activity (Todd & Marois, 2004). However, individuals varied widely in their VSTM capacity. Here, we examined the neural basis of these individual differences. A voxelwise, individualdifferences analysis revealed a significant correlation between posterior parietal cortex (PPC) activity and individuals’ VSTM storage capacity. In addition, a region-of-interest analysis indicated that other brain regions, particularly visual occipital cortex, may contribute to individual differences in VSTM capacity. Thus, although not ruling out contributions from other brain regions, the individual-differences approach supports a key role for the PPC in VSTM by demonstrating that its activity level predicts individual differences in VSTM storage capacity.     

Examining inhibition of return with onset and offset cues in the multiple-cuing paradigm

Three experiments examined inhibition of return (IOR) with onset and offset cues in a multiple-cuing paradigm. In the first two experiments, five sequential cues either appeared and remained present (onset cues) or disappeared and remained absent (offset cues). In the third experiment, the cues were either onset cues or on-off cues (appeared and then disappeared quickly after). With placeholders present, onset and offset cues produced similar declines in IOR from the most recently cued location (Experiment 1). In contrast, onset cues produced overall more IOR than on-off cues (Experiment 3). With placeholders absent (Experiment 2), no IOR was found for either onset or offset cues. The results suggest that even in a complex multiple-cuing paradigm, onsets and offsets are treated similarly by the attentional system. Furthermore, it appears that onset cues are easier to encode as previously searched than on-off cues, suggesting a role of working memory in IOR. Finally, when multiple locations are cued sequentially by onsets and offsets they must be marked by placeholders for inhibition to occur.