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PubMed2003

Determining subprocesses of visual feature search with reaction time models.

After the classic serial/parallel dichotomy of visual search mechanisms has been increasingly doubted, we investigated what search mechanisms are used between the two poles termed "pop-out" and "strictly serial search" in an overt feature search paradigm. Since reaction time slopes do not contain sufficient information for this purpose, we developed a novel technique for analyzing reaction times. Individual reaction times are modeled as sums of the durations of successive search steps. Model parameters are task characteristics (similarity, number and arrangement of target and distractors) and processing characteristics of the participant (e.g., attention dwell and shift durations). In Experiment 1, several model variants were fitted numerically to empirical reaction times. The best fitting model suggested that more than one item can be processed in a single fixation, movement of attention is abrupt and not continuous, and even in pop out search, attention is often explicitly moved to the target. In Experiment 2, we measured the central model parameter, the so-called range of attention, more directly and thereby validated the model. The model provides an explanation for the strong variation in the slope of reaction time functions, which is not based on an explicit distinction between parallel and serial search processes.

Adult↗

PubMed2002

Dynamic shifts of pigeon local/global attention.

It has previously been shown that pigeons can shift attention between parts and wholes of complex stimuli composed of larger, "global" characters constructed from smaller, "local" characters. The base-rate procedure used biased target level within any condition at either the local or global level; targets were more likely at one level than at the other. Biasing of target level in this manner demonstrated shifts of local/global attention over a time span consisting of several days with a fixed base rate. Experiment 1 examined the possibility that pigeons can shift attention between local and global levels of perceptual analysis in seconds rather than days. The experiment used priming cues the color of which predicted on a trial-by-trial basis targets at different perceptual levels. The results confirmed that pigeons, like humans, can display highly dynamic stimulus-driven shifts of local/global attention. Experiment 2 changed spatial relations between features of priming cues and features of targets within a task otherwise similar to that used in experiment 1. It was predicted that this change in cues might affect asymmetry but not the occurrence of a priming effect. A priming effect was again obtained, thereby providing generality to the claim that pigeons can learn that trial-by-trial primes predict targets at different levels of perceptual analysis. Pigeons can display perceptual, stimulus-driven priming of a highly dynamic nature.

Animals↗

PubMed1987

Influences of ACTH 4-10 on event-related potentials reflecting attention in man.

The present paper is concerned with effects of the 4-10 sequence of the endogenous ACTH on electrophysiological measures of attention in humans. It was attempted to replicate previous findings of an impaired selective attention following administration of an analog of ACTH 4-9. The effect of this analog had been found to dominate in the beginning of the blocks of an attention task, but to fade away with time on task. In the present study, fourteen male students were tested in a dichotic listening paradigm, 40 min after intranasal application of either 0.4 mg ACTH 4-10, or placebo. Averaged auditory evoked potentials (AEPs) to attended and inattended tone pips, EEG power spectra, heart rate and blood pressure, and behavioral performance were measured during task performance. ACTH 4-10 appeared to slightly impair selective attention as indicated by AEP responses. In particular, the positive shift of the AEP waveforms to inattended stimuli was reduced at the beginning of each block of tone pips under ACTH 4-10. The pattern of actions resembled the effects observed after administration of the more potent synthetic analog of ACTH 4-9 in the previous experiment. Effects of ACTH 4-10 on the AEPs to inattended stimuli, however, differed from influences of the synthetic analog in that they did not affect a rather wide latency range but concentrated on the latency range of the P200 component.

Adolescent↗

PubMed2006

Visual temporal window of integration as revealed by the visual mismatch negativity event-related potential to stimulus omissions.

We studied whether, similarly to the auditory modality, short-period temporal integration processes occur in vision. Event-related potentials (ERP) were recorded for occasional stimulus omissions from sequences of patterned visual stimuli. A posterior negative component emerged only when the constant stimulus onset asynchrony (SOA) was shorter than 150 ms. This upper limit is comparable with the duration of the temporal window of integration observed in the auditory modality (including experiments studying the effects of stimulus omissions). Parameters of the posterior negativity were highly similar irrespective of whether the stimuli were task-relevant or not (Experiment 1). Thus, we identified this potential as the visual mismatch negativity (vMMN) component, which reflects task-independent detection of violating regularities of the stimulation. vMMN was followed by an anterior positivity (the P3a), indicating attentional shifts induced by the stimulus omissions. In Experiment 2, a posterior negativity similar to that observed in Experiment 1 emerged after the termination of short trains of stimuli, again only when the SOA was shorter than 150 ms. These results support the notion of a temporal integration window in the visual modality, the duration of which is between 150 and 180 ms.

Adult↗

PubMed2006

Parkinson's disease and arithmetics: the role of executive functions.

Brain imaging studies as well as neuropsychological case studies suggest an important role for basal ganglia in arithmetic processing. Aim of this study was to assess possible numerical deficits in PD and functional relations between numerical and other cognitive deficits. Fifteen non-demented patients with early PD (stable responders treated by l-dopa) were compared to 28 healthy age and education matched controls. Both groups underwent a neuropsychological assessment focussing on numerical abilities (quantity processing, arithmetic fact retrieval, complex mental and written calculation, transcoding, arithmetic set-shifting, calculation span), working memory and executive functions. Patients with PD showed deficits in complex mental calculation and calculation span tasks. Results of this study suggest that impairments in working memory as well as in executive functions, such as inhibition of interference, lead to secondary deficits in numerical processing. The study contributes to better understanding the specific cognitive deficits in early PD and the neurocognitive architecture of arithmetic processing.

Aged↗

PubMed2005

Deficit in decision making in catatonic schizophrenia: an exploratory study.

Catatonic schizophrenia can be distinguished from paranoid schizophrenia by prominent behavioral and motor anomalies. As demonstrated in recent imaging studies, behavioral symptoms may be related to dysfunction in the ventral prefrontal cortex. However, the neuropsychological correlates of ventral prefrontal cortical dysfunction remain unclear. In an exploratory study, we investigated eight patients with catatonic schizophrenia and compared them with 19 patients with paranoid schizophrenia and 26 healthy subjects. The Iowa Gambling Task (IGT) and the Object Alternation Task (OAT) served as measures of ventral prefrontal cortical function. In addition, other prefrontal cortical tests such as a visual working memory task, a Go-NoGo task, and the Wisconsin Card Sorting Test, as well as attentional tasks, were included in the test battery. Catatonic patients showed significant deficits in the IGT characterized by an inability to shift from the initial preference for high-risk cards to a more advantageous strategy with low-risk cards. Moreover, catatonic patients showed significant deficits in the OAT. In conclusion, our preliminary results suggest a specific deficit in catatonic schizophrenia in those neuropsychological measures that are associated with ventral prefrontal cortical function.

Adult↗

PubMed2005

Effects of electrical microstimulation in monkey frontal eye field on saccades to remembered targets.

Spatially selective delay activity in the frontal eye field (FEF) is hypothesized to be part of a mechanism for the transformation of visual signals into instructions for voluntary movements. To understand the linkage between FEF activity and eye movement planning, we recorded neuronal responses of FEF neurons while monkeys performed a memory-saccade task. We then electrically stimulated the same sites during the memory-delay epoch of the task. The stimulation currents used were subthreshold for evoking saccades during a gap-fixation task. Microstimulation resulted in changes in the spatial and temporal components of saccade parameters: an increase in latency, and a shift in amplitude and direction. We performed a vector analysis to determine the relative influence of the visual cue and electrical stimulus on the memory-saccade. In general, the memory-saccade was strongly weighted toward the visual cue direction, yet the electrical stimulus introduced a consistent bias away from the receptive/movement field of the stimulation site. The effects of sub-threshold stimulation were consistent with a combination of vector subtraction and averaging, but not with vector summation. Vector subtraction may play a role in spatial updating of movement plans for memory-guided saccades when eye position changes during the memory period.

Animals↗

PubMed2001

Forebrain-specific calcineurin knockout selectively impairs bidirectional synaptic plasticity and working/episodic-like memory.

Calcineurin is a calcium-dependent protein phosphatase that has been implicated in various aspects of synaptic plasticity. By using conditional gene-targeting techniques, we created mice in which calcineurin activity is disrupted specifically in the adult forebrain. At hippocampal Schaffer collateral-CA1 synapses, LTD was significantly diminished, and there was a significant shift in the LTD/LTP modification threshold in mutant mice. Strikingly, although performance was normal in hippocampus-dependent reference memory tasks, including contextual fear conditioning and the Morris water maze, the mutant mice were impaired in hippocampus-dependent working and episodic-like memory tasks, including the delayed matching-to-place task and the radial maze task. Our results define a critical role for calcineurin in bidirectional synaptic plasticity and suggest a novel mechanistic distinction between working/episodic-like memory and reference memory.

Animals↗

PubMed2000

Effects of face inversion on the structural encoding and recognition of faces. Evidence from event-related brain potentials.

It was investigated how face inversion affects face-specific components of event-related brain potentials (ERPs) which are assumed to reflect the structural encoding and the recognition of faces. ERPs were recorded to upright and inverted photographs of familiar faces, unfamiliar faces, and houses. In Part I, participants had to detect infrequently presented targets (hands), in Part II, attention was either directed towards or away from the pictorial stimuli. When compared with upright unfamiliar faces, upright familiar faces elicited an enhanced negativity between 300 ms and 450 ms ('N400f') and an enhanced positivity between 450 and 650 ms post-stimulus ('P600f'). It is suggested that these ERP modulations are generated by processes involved in the recognition of faces. Face inversion is known to disrupt face recognition processes. Accordingly, 'N400f' and 'P600f' were generally absent in response to inverted familiar and unfamiliar faces. The face-specific N170 component at lateral posterior electrodes was not affected by face familiarity, indicating that it reflects processing stages prior to face identification. N170 was delayed and enhanced for inverted relative to upright faces. While N170 enhancements were also observed for inverted relative to upright houses, the N170 latency shift caused by stimulus inversion was face-specific. Directing attention away from the faces towards a demanding primary visual task resulted in an N170 delay for inverted as well as for upright faces, suggesting that the time course of structural encoding of faces is affected by attentional factors. These results demonstrate that ERPs can be used as electrophysiological markers of specialised brain processes underlying the structural encoding and subsequent recognition of faces.

Adolescent↗

PubMed2002

Why aggregated learning follows the power law of practice when individual learning does not: comment on Rickard (1997, 1999), Delaney et al. (1998), and Palmeri (1999).

The power law of practice is often considered a benchmark test for theories of cognitive skill acquisition. Recently, P. F. Delaney, L. M. Reder, J. J. Staszewski, and F. E. Ritter (1998), T. J. Palmeri (1999), and T. C. Rickard (1997, 1999) have challenged its validity by showing that empirical data can systematically deviate from power-function fits. The main purpose of the present article is to extend their explanations in two ways. First, the authors empirically show that abrupt changes in performance are not necessarily based on a shift from algorithm to memory-based processing, but rather and more generally, that they occur whenever a more efficient task strategy is generated. Second, the authors show mathematically and per simulation that power functions can perfectly fit aggregated learning curves even when all underlying individual curves are discontinuous. Therefore, the authors question conclusions drawn from fits to aggregated data.

Humans↗

PubMed2005

Discrimination of multidimensional visual stimuli by mice: intra- and extradimensional shifts.

A visual discrimination protocol similar to that used with monkeys was adapted to measure attentional set-shifting in mice. An automated touchscreen procedure with compound visual stimuli was used to train mice to attend to 1 of 2 stimulus dimensions (lines or shapes). On a 2nd problem with new stimuli, the mice were required to attend to the same dimension (intradimensional [ID] shift) or switch to the previously irrelevant dimension (extradimensional [ED] shift). Mice readily learned the initial compound discrimination and following shift problem, but there was no ID-ED difference. The fact that mice can be tested with stimuli and task sequences similar to those used with primates suggests that this method can be used to directly compare higher cognitive functions in diverse species.

Animals↗

PubMed2005

Social cues shift functional connectivity in the hypothalamus.

We determined how social stimuli that vary in behavioral relevance differentially activate functional networks in the frog hypothalamus. As measured by egr-1 mRNA levels, activity in three hypothalamic nuclei varied with acoustic stimulus, and these responses were correlated with egr-1 responses in different auditory regions regardless of stimulus. The correlations among hypothalamic nuclei, however, varied as a function of the behavioral relevance of the stimuli. Thus relevant social cues shift the functional connectivity within the hypothalamus, consistent with principles that underlie the simultaneous processing of sensory information in cognitive tasks.

Acoustic Stimulation↗

PubMed1994

Influence of thiamine on the behavioral sensitivity to ethanol.

Changes in sensitivity to ethanol's rate-decreasing effects on operant performance were examined in control rats and cohorts that received diet-induced or diet+pyrithiamine-induced thiamine deficiency. Seven groups of male Sprague-Dawley rats (12 rats/group) were trained in a 5-cycle lever-press operant task under a fixed-ratio 30 schedule of food reinforcement. Once trained to maintain consistent operant performance across all 5 cycles, each rat was tested with various doses of ethanol injected at the beginning of each time-out cycle. Each group of rats demonstrated equivalent saline baseline operant performance and ED50 for ethanol's rate-suppressing effects. Training sessions were suspended and rats received either a short- (9 days) or long-term (5-week) exposure to regular rat chow diet or thiamine-deficient diet, and received either saline or pyrithiamine injections in a 2 x 2 design. Three additional control groups were maintained on a regular rat chow diet and received supplemental injections of either thiamine+pyrithiamine injections, thiamine+saline injections, or saline+pyrithiamine injections. The controlled diet phase continued until the development of overt signs of thiamine deficiency, at which time thiamine supplements were administered for 4 days. In phase 3, all rats were retrained in the operant task and a second ethanol dose-effect function was generated. A history of thiamine deficiency and recovery failed to shift the behavioral dose-effect functions significantly for ethanol and their associated blood alcohol curves. Most interestingly, significant behavioral sensitization to ethanol's rate suppressant effects was demonstrated in the two control groups of rats receiving regular rat chow diet in combination with supplemental injections of thiamine and either saline or pyrithiamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcoholic Intoxication↗

PubMed1999

Transforming negative parent-adolescent interactions: from impasse to dialogue.

This treatment development, process research study focuses on resolving in-session, parent-adolescent conflicts characterized by negative exchanges, emotional disengagement, and poor problem solving. These processes have been empirically linked to poor developmental outcomes, and clinically linked to poor therapeutic progress. Specifically, we examined how a shift of therapeutic focus from behavior management to interpersonal relationship failures could resolve this impasse and resuscitate therapeutic momentum. A task analysis approach was used to verify the presence of the impasse, to illuminate its core features, and to define the therapist and client behaviors associated with resolving it. In Part 1 of this two-part series, we presented the final performance map that represented that family's cognitive, emotional and behavioral interactions necessary to resolve the impasse. This article, Part II, focuses on the theoretical foundation of the intervention strategies, the phenomenology of the impasse, and the therapist's skills needed to facilitate it.

Adolescent↗

PubMed1999

Misrepresentation of horizontal space in left unilateral neglect: role of hemianopia.

BACKGROUND: Right-brain-damaged patients with left unilateral neglect are reported to misperceive the horizontal extension of contralesional stimuli as being shorter than that of ipsilesional stimuli. OBJECTIVE: To investigate the functional and anatomic correlates of horizontal space misrepresentation. METHODS: Eight right-brain-damaged patients with contralesional neglect and complete hemianopia (N+H+), nine right-brain-damaged patients with contralesional neglect and no visual field defect (N+H-), and five unilateral brain-damaged patients with contralesional complete hemianopia and no neglect (N-H+) reproduced a horizontal distance (10 cm) in the contralesional and ipsilesional hemispace. RESULTS: N+H+ patients overextended the distance contralesionally and underextended the same distance ipsilesionally. N+H- and N-H+ patients reproduced equivalent distances contralesionally and ipsilesionally. Compared with N+H- patients, N+H+ patients had a greater ipsilesional shift when bisecting horizontal lines; however, these two groups of patients had comparable neglect severity on multiple-item cancellation tasks. In the N+H+ group the area of maximal overlapping of the lesion was in the posterior cerebral lobes. CONCLUSION: Complete contralesional hemianopia after posterior brain damage is an important factor in determining misrepresentation of horizontal space in patients with left unilateral neglect.

Adult↗

PubMed2002

From operating theatre to operating studio--visualizing surgery in the age of telemedicine.

We have conducted a telemedicine project between two of Norway's largest hospitals (Rikshospitalet and Ullevål Hospital) with a focus on image-guided surgical and radiological procedures. Video was broadcast using a 34 Mbit/s ATM network. This resulted in changes in the local work practice to accommodate and facilitate the communication. It also required changes to the surgeon's tasks to improve communication with remote viewers. These changes were not trivial and can be viewed as signs of a shift towards a more public kind of surgery and interventional radiology, brought about by new technology.

Education, Distance↗

PubMed1994

Classification and perceived similarity of compound gratings that differ in relative spatial phase.

Discrimination studies suggest that two, and only two, channels encode relative spatial phase shifts in compound gratings (Bennett & Banks, 1991; Field & Nachmias, 1984). The more sensitive channel consists of even-symmetric filters and responds best to cosine phase shifts (e.g., 0 degree-180 degrees); the other consists of odd-symmetric filters and responds best to sine phase shifts (e.g., 90 degrees-270 degrees). The present experiments investigated whether the two-channel model generalizes to suprathreshold perceptual tasks. Experiment 1 examined classification learning of compound gratings, consisting of a fundamental (f) and second harmonic (2f), that differed in 2f contrast and relative phase. Experiments 2 and 3 measured the perceived similarity of f + 2f gratings. The results of Experiment 1 were broadly consistent with the predictions of the two-channel model. Specifically, the classification data were best explained by assuming that classification was based on the responses of differentially sensitive even- and odd-symmetric filters. In Experiments 2 and 3, two-dimensional multidimensional scaling solutions provided a good account for the similarity judgments. In Experiment 2, Dimension 1 was strongly correlated with cosine phase, and Dimension 2 was moderately correlated with sine phase. In Experiment 3, cosine phase was again strongly related to Dimension 1, whereas the absolute value of sine phase was strongly related to Dimension 2. Overall, these results suggest that the two-channel model of phase discrimination provides a useful framework for interpreting classification and similarity judgments of compound gratings.

Adult↗

PubMed1975

Low-IQ deficit in intradimensional discrimination shift despite overtraining and verbal feedback.

One hundred and twenty low-IQ and average-IQ children (MA 5 to 7 years) were required to learn a 2-choice discrimination involving verbal and manual responses, with verbal correction of errors, before proceeding to an intradimensional shift with new color cues. One-half of each group also received 100 interpolated trials (overtraining) on the original task. Results disclosed a low-IQ deficit during original learning, which was absent during overtraining but recurred in the final phase, undiminished by either overtraining or verbal feedback conditions applied during the transfer phase. The findings oppose a theoretical explanation based on probability of attending to color, since the inference that this probability approximated 1 for all subjects was amply justified, thus emphasizing the need for alternative interpretations of the retarded subjects' difficulty.

Attention↗