Petra M.J. Pollux

Behavioural and physiological correlates of impulsivity in the domestic dog (Canis familiaris)

Impulsivity is a trait related to inhibitory control which is expressed in a range of behaviours. Impulsive individuals show a decreased ability to tolerate delay of reinforcement, and more impulsive behaviour has been linked to decreased levels of serotonin and dopamine in a number of species. In domestic dogs, impulsivity is implicated in problem behaviours that result from a lack of self control, but currently there are no published studies that assess behavioural and physiological measures of impulsivity in relation to this trait. Impulsivity scores were calculated for 41 dogs using an owner-report assessment, the Dog Impulsivity Assessment Scale (DIAS). Twenty-three of these subjects completed an operant choice task based on a delayed reward paradigm, to assess their tolerance to delay of reinforcement. High Pressure Liquid Chromatography (HPLC) with Fluorometric Detection was used to detect levels of the metabolites of serotonin (5-HIAA) and dopamine (HVA) in the urine of 17 of the subjects. Higher impulsivity scores were found to be significantly correlated with more impulsive behaviour (reduced tolerance to delay of reinforcement) in the behaviour tests and lower levels of urinary 5-HIAA and 5-HIAA/HVA ratio. The results demonstrate convergent validity between impulsivity (as assessed by the DIAS) and behavioural and physiological parameters.

Advance preparation of set-switches in Parkinson’s disease

Eighteen patients with Parkinsons disease (PD) and 18 healthy control subjects were presented with a switching task where stimuli elicited either one (no-conflict condition) or two (conflict condition) task-relevant stimulus-response mappings. The response stimulus interval (RSI) between trials was varied to allow investigation of the extent to which participants engaged in advanced preparation of task set. In line with previous findings, set-switching deficits of PD patients were only observed in the conflict condition. Prolonging the RSI led to a reduction of switch costs for control subjects in both the conflict and the no-conflict task, whereas this effect was attenuated for PD patients in the conflict condition. This deficit was explained in terms of a reduced ability to maintain cue-action representations active in working memory in high interference conditions, and was related to the possible role of the frontostriatal circuit in maintaining focussed attention.

Voluntary and automatic visual spatial shifts of attention in Parkinson's disease: An analysis of costs and benefits

Visual spatial shifts of attention were investigated in 13 patients suffering from Parkinsons disease and 20 control subjects. Attention was directed towards a target location with peripheral or central cues at varying SOAs in two separate experiments. A benefit and cost analysis was conducted on reaction times. The results of the central cueing task showed that in comparison with control subjects, costs of invalid cueing were reduced in patients. Results of the peripheral cueing task revealed that although the cueing effect (validin valid) was similar for patients and controls, the effect of valid cueing (neutral valid) was greater in patients. The effects observed in both tasks were explained as an impaired ability of patients with Parkinsons disease to maintain attention.

Beliefs about Alzheimer's disease in Britain

Objectives: Alzheimers disease (AD) represents one of the most debilitating conditions affecting the elderly. Despite the prevalence and consequences of AD, surveys have revealed that the general public in North America and Australia hold numerous misconceptions of the disease. The aim of this study was to examine whether misconceptions of AD are also endorsed by adults in Britain. Method: The Alzheimers disease knowledge scale (ADKS) was completed by 312 adults residing in Lincolnshire, UK. The ADKS contains 30 true or false statements pertaining to risk factors, assessment and diagnosis, symptoms, course, life impact, caregiving, and treatment and management of AD. Results: Regardless of age, education, and familiarity with AD, respondents in this survey demonstrated a good understanding (≥80% mean correct) of some items from all categories. However, knowledge gaps exist about the course of the disease, and of conditions that can exacerbate (inadequate nutrition) or simulate (depression) the symptoms of AD. Moreover, a large proportion of respondents (∼75%) are unaware that hypertension or hypercholesterolemia may increase ones predisposition to developing AD. Conclusion: Respondents revealed knowledge gaps pertaining to conditions that masquerade as AD, increase ones vulnerability to AD, and exacerbate AD symtomatology. Educational campaigns that specifically target these issues may help reduce the impact of AD.

Reduced Task-Set Inertia in Parkinson’s Disease

This study investigated the relationship between cognitive inhibition and set-switching costs in 13 patients with Parkinson’s disease (PD) and 16 control subjects using a set-switching task with fully predictable switches. Incongruent colour-words and numerals were presented in either baseline (only colour-words or only numerals) or alternating lists (colour-words and numerals in alternation). Words required either a word-reading or colour-naming response whereas numerals required either a value-naming (value of the digits) or group-size naming (number of digits) response. Stroop interference was found to be increased and practice effects on nondominant tasks reduced in PD patients, suggesting that the ability to increase control over interference from irrelevant prepotent responses may be implicated in PD. Switch costs of PD patients were reduced on the first few trials of alternating dominant task lists and increased towards the end of alternating nondominant task lists. Both effects were explained as resulting from a reduced ability to maintain task-sets where selection of correct responses relies on inhibition of irrelevant stimulus-response mappings.

Facial expression training optimises viewing strategy in children and adults.

This study investigated whether training-related improvements in facial expression categorization are facilitated by spontaneous changes in gaze behaviour in adults and nine-year old children. Four sessions of a self-paced, free-viewing training task required participants to categorize happy, sad and fear expressions with varying intensities. No instructions about eye movements were given. Eye-movements were recorded in the first and fourth training session. New faces were introduced in session four to establish transfer-effects of learning. Adults focused most on the eyes in all sessions and increased expression categorization accuracy after training coincided with a strengthening of this eye-bias in gaze allocation. In children, training-related behavioural improvements coincided with an overall shift in gaze-focus towards the eyes (resulting in more adult-like gaze-distributions) and towards the mouth for happy faces in the second fixation. Gaze-distributions were not influenced by the expression intensity or by the introduction of new faces. It was proposed that training enhanced the use of a uniform, predominantly eyes-biased, gaze strategy in children in order to optimise extraction of relevant cues for discrimination between subtle facial expressions.

Additive effects of inhibiting attention to objects and locations in three-dimensional displays

One of the processes thought to underlie visual selection works by biasing attention away from either recently examined locations or objects. The extent of this “inhibition” is greatest when the inhibited object and the inhibited location coincide. In Experiment 1, rectangles are presented stereoscopically at different depths but at similar positions horizontally and vertically. Here, any inhibition should be based solely on a spatial code, as the objects, the rectangles are clearly separate objects. In Experiment 2, the corners of the rectangles are joined to produce a single cuboid that extends in depth space. Now inhibition based on both spatial and object codes should be seen because even when on different depth planes the cue and target are associated with the same object. Consistent with our understanding of the additive effects of inhibition of space and object codes, the extent of inhibition in the second study is almost double that of the first. The results further suggest that space-based inhibition operates within a two-dimensional representation while object-based inhibition utilizes a three-dimensional representation.

Exploitation of natural geometrical regularities facilitates target detection

We have evolved to operate within a dynamic visual world in which natural visual signals are not random but have various statistical regularities. Our rich experience of the probability structure of these regularities could influence visual computation. Considering that spatiotemporal regularity, co-linearity and co-circularity are common geometrical regularities in natural scenes, we explored how our visual system exploits these regularities to achieve accurate and efficient representations of the external world. By measuring human contrast detection performance of a briefly presented foveal target embedded in dynamic stimulus sequences (comprising six short bars appearing consecutively towards the fovea) imitating common regularity structures, we found that both contrast sensitivity and reaction time for target detection was facilitated by predictable spatiotemporal stimulus structure. Qualitatively consistent with natural image analysis that co-linearity is a stronger statistical feature than co-circularity, the facilitation in target detection was more evident for predictable stimulus sequences following a co-linear path than a co-circular path. Control experiments further showed that response bias and uncertainty reduction could not fully account for our observation. It seems that our visual system exploits geometrical natural regularities to facilitate the interpretation of incoming visual signals, such as constraining interpretation on the basis of contextual priors.

VEP Responses to Op-Art Stimuli.

Several types of striped patterns have been reported to cause adverse sensations described as visual discomfort. Previous research using op-art-based stimuli has demonstrated that spurious eye movement signals can cause the experience of illusory motion, or shimmering effects, which might be perceived as uncomfortable. Whilst the shimmering effects are one cause of discomfort, another possible contributor to discomfort is excessive neural responses: As striped patterns do not have the statistical redundancy typical of natural images, they are perhaps unable to be encoded efficiently. If this is the case, then this should be seen in the amplitude of the EEG response. This study found that stimuli that were judged to be most comfortable were also those with the lowest EEG amplitude. This provides some support for the idea that excessive neural responses might also contribute to discomfort judgements in normal populations, in stimuli controlled for perceived contrast.

Improved categorization of subtle facial expressions modulates Late Positive Potential.

Biases in facial expression recognition can be reduced successfully using feedback-based training tasks. Here we investigate with event-related potentials (ERPs) at which stages of stimulus processing emotion-related modulations are influenced by training. Categorization of subtle facial expressions (morphed from neutral to happy, sad or surprise) was trained with correct-response feedback on each trial. ERPs were recorded before and after training while participants categorized facial expressions without response feedback. Behavioral data demonstrated large improvements in categorization of subtle facial expression which transferred to new face models not used during training. ERPs were modulated by training from 450 ms post-stimulus onward, characterized by a more gradual increase in P3b/Late Positive Potential (LPP) amplitude as expression intensity increased. This effect was indistinguishable for faces used for training and for new faces. It was proposed that training elicited a more fine-grained analysis of facial information for all subtle expressions, resulting in improved recognition and enhanced emotional motivational salience (reflected in P3b/LPP amplitude) of faces previously categorized as expressing no emotion.