Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Beyond liking : emotional and physiological responses to food stimuli
    He, W. - \ 2016
    Wageningen University. Promotor(en): Kees de Graaf, co-promotor(en): Sanne Boesveldt; Rene de Wijk. - Wageningen : Wageningen University - ISBN 9789462576506 - 149
    stimuli - food - emotions - autonomic nervous system - odours - taste - beverages - physiological functions - man - human behaviour - expressivity - prikkels - voedsel - emoties - autonome zenuwstelsel - geurstoffen - smaak - dranken - fysiologische functies - mens - menselijk gedrag - expressiviteit

    Background and aim

    Traditional liking ratings are typically seen as an important determinant in eating behavior. However, in order to better understand eating behavior, we need to first better understand (the dynamic and implicit features underlying) liking appraisal. The aim of this thesis was to investigate the effects of food stimuli varying in sensory modality (smell and taste), pleasantness and intensity, on emotional and physiological responses leading up to liking appraisal.


    Four studies, using healthy participants, were conducted as part of this thesis. In the first study, responses to pleasant versus unpleasant food odors varying in intensity were measured discretely using pleasantness ratings, intensity ratings and non-verbally reported emotions (PrEmo), as well as continuously using facial expressions and autonomic nervous system (ANS) responses. To further explore how explicit and implicit factors contribute to pleasantness appraisal, the same measures were assessed in response to food odors with a wider range of valence. Next, we focused on facial expressions and ANS responses elicited by single sips of breakfast drinks that were equally liked. In the last study, we investigated changes in pleasantness after consuming semi-liquid meals to (sensory-specific) satiety, combined with measures of facial expressions and ANS responses.


    Both non-verbal reported emotions and emotional facial expressions were demonstrated to be able to discriminate between food odors differing in pleasantness and between food odors differing in intensity. In addition to discrete emotional responses, odor valence associated best with facial expressions after 1 second of odor exposure. Furthermore, facial expressions and ANS responses measured continuously were found odor-specific in different rates over time. Results of food odors with a wider range of valence showed that non-verbally reported emotions, facial expressions and ANS responses correlated with each other best in different time windows after odor presentation: facial expressions and ANS responses correlated best with the explicit emotions of the arousal dimension in the 2nd second of odor presentation, whereas later ANS responses correlated best with the explicit emotions of the valence dimension in the 4th second. For food stimuli varying in flavor (breakfast drinks), facial expressions and ANS responses showed strongest associations with liking after 1 second of tasting, as well as with intensity after 2 seconds of tasting. Lastly, we were able to demonstrate that ANS responses, as well as facial expressions of anger and disgust were associated with satiety. Further effects of sensory-specific satiety were also reflected by skin conductance, skin temperature, as well as facial expressions of sadness and anger.


    Both non-verbal reported emotions and emotional facial expressions were demonstrated to be able to discriminate between food odors differing in pleasantness and/or intensity. Explicit and implicit emotional responses, as well as physiological patterns are related to liking appraisals involved in smelling foods. Implicit measures such as facial expressions and ANS responses can provide more multidimensional information for both food odors and tastes than explicit measures and prove to be highly dynamic over time with specific time courses. Early implicit facial and ANS responses primarily reflect emotion arousal, whereas later ANS responses reflect emotion valence, suggesting dynamic unfolding of different appraisals of food stimuli. Furthermore, ANS responses and facial expressions can reflect pleasantness, satiety, and a combination of both: sensory-specific satiety. This suggests that implicit processes play an important role in dynamic liking appraisals with respect to eating behavior.

    Stimuli for municipal responses to climate adaptation: insights from Philadelphia – an early adapter
    Uittenbroek, C.J. ; Janssen-Jansen, Leonie ; Runhaar, H.A.C. - \ 2016
    International Journal of Climate change Strategies and Management 8 (2016)1. - ISSN 1756-8692 - p. 38 - 56.
    climate adaptation - stimuli - governance approaches - Philadelphia - institutional entrepreneurship - political leadership
    An in-depth understanding of these stimuli is currently lacking in literature as most research has focussed on overcoming barriers to climate adaptation. The aim of this paper is to identify stimuli for municipal responses to climate adaptation and examine how they influence the governance approach to addressing climate adaptation through explorative case study research. Fort this, an early adapter was selected as case: Philadelphia (USA). By reconstructing the organization of two municipal responses to climate adaptation in this city, we have been able to identify stimuli and gain insight in the city’s governance approach. The reconstruction is based on data triangulation that consists of semi-structured interviews with actors involved in these responses, policy documents and newspaper articles. The research illustrates the importance of stimuli such as strategically framing climate adaptation within wider urban agendas, political leadership and institutional entrepreneurs. Moreover the research reveals that it is the combination of stimuli that influences the governance approach to climate adaptation. Some stimuli will trigger a dedicated approach to climate adaptation, while others initiate a mainstreaming approach. This research is important especially to municipalities to recognize stimuli within their own (policy) context and subsequently, make informed decisions to exploit all or some of these stimuli to initiate a governance approach to climate adaptation.
    Altered food-cue processing in chronically ill and recovered women with anorexia nervosa
    Sanders, N. ; Smeets, P.A.M. ; Elburg, A.A. van; Danner, U.N. ; Meer, F. van; Hoek, H.W. ; Adan, R.A.H. - \ 2015
    Frontiers in Behavioral Neuroscience 9 (2015). - ISSN 1662-5153 - 12 p.
    default mode network - high-calorie foods - eating-disorders - functional-anatomy - reward - fmri - stimuli - leptin - energy - cortex
    Anorexia nervosa (AN) is a severe mental disorder characterized by food restriction and weight loss. This study aimed to test the model posed by Brooks et al. (2012a,b) that women suffering from chronic AN show decreased food-cue processing activity in brain regions associated with energy balance and food reward (bottom-up; BU) and increased activity in brain regions associated with cognitive control (top-down; TD) when compared with long-term recovered AN (REC) and healthy controls (HC). Three groups of women, 15 AN (mean illness duration 7.8 ± 4.1 years), 14 REC (mean duration of recovery 4.7 ± 2.7 years) and 15 HC viewed alternating blocks of food and non-food images preceded by a short instruction during functional magnetic resonance imaging (fMRI), after fasting overnight. Functional region of interests (fROIs) were defined in BU (e.g., striatum, hippocampus, amygdala, hypothalamus, and cerebellum), TD (e.g., medial and lateral prefrontal cortex, and anterior cingulate), the insula, and visual processing areas (VPA). Food-cue processing activation was extracted from all fROIs and compared between the groups. In addition, functional connectivity between the fROIs was examined by modular partitioning of the correlation matrix of all fROIs. We could not confirm the hypothesis that BU areas are activated to a lesser extent in AN upon visual processing of food images. Among the BU areas the caudate showed higher activation in both patient groups compared to HC. In accordance with Brooks et al.’s model, we did find evidence for increased TD control in AN and REC. The functional connectivity analysis yielded two clusters in HC and REC, but three clusters in AN. In HC, fROIs across BU, TD, and VPA areas clustered; in AN, one cluster span across BU, TD, and insula; one across BU, TD, and VPA areas; and one was confined to the VPA network. In REC, BU, TD, and VPA or VPA and insula clustered. In conclusion, despite weight recovery, neural processing of food cues is also altered in recovered AN patients.
    Odors: appetizing or satiating? Development of appetite during odor exposure over time
    Ramaekers, M.G. ; Boesveldt, S. ; Lakemond, C.M.M. ; Boekel, M.A.J.S. van; Luning, P.A. - \ 2014
    International Journal of Obesity 38 (2014). - ISSN 0307-0565 - p. 650 - 656.
    sensory-specific satiety - cephalic phase responses - food-cue exposure - dietary restraint - chewing gum - perception - humans - stimuli - flavor - meal
    Background: Exposure to palatable food odors influences appetite responses, either promoting or inhibiting food intake. Possibly, food odors are appetizing after a short exposure (of circa 1–3¿min), but become satiating over time (circa 10–20¿min). Objective: To investigate the effect of odor exposure on general appetite and sensory-specific appetite (SSA) over time. Design: In a cross-over study, 21 unrestrained women (age: 18–45 years; BMI: 18.5–25¿kg¿m-2) were exposed for 20¿min to eight different odor types: five food odors, two nonfood odors and no-odor. All odors were distributed in a test room at suprathreshold levels. General appetite, SSA and salivation were measured over time. Results: All food odors significantly increased general appetite and SSA, compared with the no-odor condition. The nonfood odors decreased general appetite. All effects did not change over time during odor exposure. Savory odors increased the appetite for savory foods, but decreased appetite for sweet foods, and vice versa after exposure to sweet odors. Neither food odors nor nonfood odors affected salivation. Conclusions: Palatable food odors were appetizing during and after odor exposure and did not become satiating over a 20-min period. Food odors had a large impact on SSA and a small impact on general appetite. Moreover, exposure to food odors increased the appetite for congruent foods, but decreased the appetite for incongruent foods. It may be hypothesized that, once the body is prepared for intake of a certain food with a particular macronutrient composition, it is unfavorable to consume foods that are very different from the cued food.
    Learning about the energy density of liquid and semi-solid foods
    Hogenkamp, P.S. ; Stafleu, A. ; Mars, M. ; Graaf, C. de - \ 2012
    International Journal of Obesity 36 (2012)9. - ISSN 0307-0565 - p. 1229 - 1235.
    satiation - satiety - humans - compensation - viscosity - carbohydrate - responses - behavior - stimuli - flavor
    BACKGROUND: People learn about a food's satiating capacity by exposure and consequently adjust their energy intake. OBJECTIVE: To investigate the effect of energy density and texture on subsequent energy intake adjustments during repeated consumption. DESIGN: In a randomized crossover design, participants (n = 27, age: 21 +/- 2.4 years, body mass index: 22.2 +/- 1.6 kg m(-2)) repeatedly consumed highly novel foods that were either low-energy-dense (LE: 30 kcal per 100 g) or high-energy-dense (HE: 130 kcal per 100 g), and either liquid or semi-solid, resulting in four product conditions. In each condition, a fixed portion of test food was consumed nine times as an obligatory part of breakfast, lunch and dinner on 3 consecutive days. All meals continued with an ad libitum buffet; food items for evening consumption were provided and the intake (kcal per day) was measured. RESULTS: Buffet intake depended on energy density and day of consumption of the test foods (day*energy interaction: P = 0.02); daily buffet intake increased from day 1 (1745 +/- 577 kcal) to day 3 (1979 +/- 567 kcal) in the LE conditions; intake did not change in the HE conditions (day 1: 1523 +/- 429 kcal, day 3: 1589 +/- 424 kcal). Food texture did not affect the intake (P = 0.56). CONCLUSIONS: Intake did depend on energy density of the test foods; participants increased their buffet intake over days in response to learning about the satiating capacity of the LE foods, but did not change buffet intake over days when repeatedly consuming a HE food as part of their meal. The adjustments in intake were made irrespective of the food texture.
    Individually Modified Saliva Delivery Changes the Perceived Intensity of Saltiness and Sourness
    Heinzerling, C.I. ; Stieger, M.A. ; Bult, J.H.F. ; Smit, B. - \ 2011
    Chemosensory Perception 4 (2011)4. - ISSN 1936-5802 - p. 145 - 153.
    flow-rate - taste sensitivity - alpha-amylase - perception - secretion - stimuli - texture - starch - acids - ph
    Individuals vary largely in their salivary flow and composition, and given the importance of saliva on perception of taste, this might influence how the tastant stimuli are perceived. We therefore hypothesise that altering the individual salivary flow rates has an impact on the perceived taste intensity. In this study, we investigated the role of saliva amount on the perceived taste intensity by excluding parotid saliva and adding artificial saliva close to the parotid duct at preset flow rates. Significant decreases in perception with increasing salivary flow rates were observed for citric acid and sodium chloride. This can partially be explained by a dilution effect which is in line with previous studies on detectable concentration differences. However, since the bitterness and sweetness remained unaffected by the salivary flow conditions and the dilution effect was comparable to that of saltiness, further explanation is needed. Furthermore, we investigated whether the suppression of taste intensity in binary mixtures (taste–taste interactions) could possibly be caused by the increased salivary flow rate induced by an additional taste attribute. The results show, however, that suppression of taste intensity in binary mixtures was not affected by the rate of salivation. This was more likely to be explained by psychophysics
    The fish is bad: negative food odors elicit faster and more accurate reactions than other odors
    Boesveldt, S. ; Frasnelli, J. ; Gordon, A. ; Lundstrom, J.N. - \ 2010
    Biological Psychology 84 (2010)2. - ISSN 0301-0511 - p. 313 - 317.
    unpleasant odor - autonomic parameters - responses - fear - pleasant - stimuli - emotion - humans - perception - attention
    Dissociating between ‘good’ or ‘bad’ odors is arguable of crucial value for human survival, since unpleasant odors often signal danger. Therefore, negative odors demand a faster response in order to quickly avoid or move away from negative situations. We know from other sensory systems that this effect is most evident for stimuli from ecologically-relevant categories. In the olfactory system the classification of odors into the food or non-food category is of eminent importance. We therefore aimed to explore the link between odor processing speed and accuracy and odor edibility and valence by assessing response time and detection accuracy. We observed that reaction time and detection accuracy are influenced by both pleasantness and edibility. Specifically, we showed that an unpleasant food odor is detected faster and more accurately than odors of other categories. These results suggest that the olfactory system reacts faster and more accurately to ecologically-relevant stimuli that signal a potential danger
    Intake during repeated exposure to low- and high-energy-dense yogurts by different means of consumption
    Hogenkamp, P.S. ; Mars, M. ; Stafleu, A. ; Graaf, C. de - \ 2010
    American Journal of Clinical Nutrition 91 (2010)4. - ISSN 0002-9165 - p. 841 - 847.
    food-intake - eating behavior - young-children - satiety - compensation - satiation - carbohydrate - appetite - stimuli - humans
    Background: An important question in the regulation of energy intake is whether dietary learning of energy content depends on the food's characteristics, such as texture. Texture might affect the duration of sensory exposure and eating rate. Objective: The objective was to investigate whether a long sensory exposure, due to differences in means of consumption and in viscosity, enhances learned associations between sensory signals and metabolic consequences and hence facilitates energy intake compensation. Design: A total of 105 healthy young adults with a mean (±SD) age of 22 ± 3 y and a body mass index (in kg/m2) of 21.6 ± 1.7 participated in a parallel intervention in 3 groups: liquid yogurt with a straw (liquid/straw; n = 34), liquid yogurt with a spoon (liquid/spoon; n = 36), or semisolid yogurt with a spoon (semisolid/spoon; n = 35). Novel flavored yogurts were offered ad libitum for breakfast in 2 energy densities: low (215 kJ/100 g) and high (600 kJ/100 g). Subjects were repeatedly exposed to the yogurt products (10 times), and yogurt intake was measured. Results: Intakes (P = 0.01) and eating rates (P = 0.01) were highest in the liquid/straw group. Average intakes over 10 exposures were 575 ± 260 g for liquid/straw, 475 ± 192 g for liquid/spoon, and 470 ± 223 g for semisolid/spoon; average eating rates were 132 ± 83 g/min for liquid/straw, 106 ± 53 g/min for liquid/spoon, and 105 ± 88 g/min for semisolid/spoon. No significant interaction for intake between intervention group, energy density, and repeated exposure was observed, and intakes of the low- and high-energy-dense yogurts did not change over time in any of the intervention groups. Conclusions: We observed no energy intake compensation after repeated exposure to yogurt products. Differences in ad libitum yogurt intake could be explained by eating rate, which was affected by the different means of consumption. This trial was registered with the Dutch trial registration at as NTR1853.
    Facial expressions in school-aged children are a good indicator of 'dislikes', but not of 'likes'
    Zeinstra, G.G. ; Koelen, M.A. ; Colindres, D. ; Kok, F.J. ; Graaf, C. de - \ 2009
    Food Quality and Preference 20 (2009)8. - ISSN 0950-3293 - p. 620 - 624.
    food preferences - hedonic impact - basic tastes - perspective - stimuli - emotion - infants - valence - gender
    Our pilot study sought to investigate whether facial expressions are a suitable and accurate method to assess food preferences in school-aged children. Six children, aged 5–13 years, tasted seven stimuli in randomized order: apple, sauerkraut, and beetroot juice, skimmed milk, asparagus solution, a bitter and a sweet solution. Their preferences were assessed using a traditional rank order procedure. Each tasting was video-recorded to capture facial expressions. The first six seconds after tasting were coded using a selection of FACS-system Action Units (AUs). Data were analysed by frequency count, Pearson correlations and Chi-Square test. For disliked liquids, the majority of the AUs displayed were negative, whereas for neutral and liked liquids the number of positive and negative AUs was similar. On the basis of our results, we conclude that facial expressions are suitable to measure dislike, but not suitable to measure various gradients of food acceptance in children aged 5–13 years.
    Differential responses of Nile tilapia (Oreochromis niloticus) to fin clip wounding and related stress: perspectives
    Abbink, W. ; Roques, J. ; Geurds, F. ; Vis, J.W. van de - \ 2009
    Yerseke : IMARES (Report / IMARES Wageningen UR C133/09) - 25
    aquacultuur - dierenwelzijn - pijn - prikkels - perceptie - onderzoek - visfauna - aquaculture - animal welfare - pain - stimuli - perception - research - fish fauna
    The debate around fish welfare is intensifying in The Netherlands. As a result, more research is carried out to enhance knowledge on fish welfare in aquaculture. Detailed information is lacking on how production procedures causing discomfort to the fish may affect welfare. That fish must perceive adversive stimuli follows from the fact that nociceptive mechanisms similar to those in mammals are present in fish. However, whether and how nociceptive stimuli are perceived or interpreted by a fish is a far more difficult question that requires significantly more effort from fundamental research, both neurophysiological and behavioural studies, than now available. The study presented in this report aimed to define selected readout for the acute response to a supposedly painful stimulus: a standardised tailfin clip to a common carp. In conclusion, we succeeded to demonstrate differential, stronger responses to a presumed painful stimulus than to the handling stress per se associated with the administration of the pain stimulus. These parameters will be the focus of future research within this welfare project.
    Temporal contrast of salt delivery in mouth increases salt perception
    Busch, J.L.H.C. ; Tournier, C. ; Knoop, J.E. ; Kooyman, G. ; Smit, G. - \ 2009
    Chemical Senses 34 (2009)4. - ISSN 0379-864X - p. 341 - 348.
    flavor release - chorda tympani - gustatory adaptation - time-intensity - taste - sweeteners - sweetness - stimuli - system - gels
    The impact of salt delivery in mouth on salt perception was investigated. It was hypothesized that fast concentration changes in the delivery to the receptor can reduce sensory adaptation, leading to an increased taste perception. Saltiness ratings were scored by a panel over time during various stimulation conditions involving relative changes in NaCl concentration of 20% and 38%. Changes in salt delivery profile had similar effect on saltiness perception when delivered either by a sipwise method or by a gustometer. The impact of concentration variations and frequency of concentration changes was further investigated with the gustometer method. Five second boosts and 2 s pulses were delivered during 3 sequential 10-s intervals, whereas the delivered total salt content was the same for all conditions. Two second pulses were found to increase saltiness perception, but only when the pulses were delivered during the first seconds of stimulation. Results suggest that the frequency, timing, and concentration differences of salt stimuli can affect saltiness. Specifically, a short and intense stimulus can increase salt perception, possibly through a reduction of adaptation.
    Startle response of captive North Sea fish species to underwater tones between 0.1 and 64 kHz
    Kastelein, R.A. ; Heul, S. van der; Verboom, W.C. ; Jennings, N. ; Veen, J. van der; Haan, D. de - \ 2008
    Marine Environmental Research 65 (2008)5. - ISSN 0141-1136 - p. 369 - 377.
    cod gadus-morhua - directional hearing - behavior - sound - thresholds - ultrasound - stimuli - noise - field
    World-wide, underwater background noise levels are increasing due to anthropogenic activities. Little is known about the effects of anthropogenic noise on marine fish, and information is needed to predict any negative effects. Behavioural startle response thresholds were determined for eight marine fish species, held in a large tank, to tones of 0.1-64 kHz. Response threshold levels varied per frequency within and between species. For sea bass, the 50% reaction threshold occurred for signals of 0.1-0.7 kHz, for thicklip mullet 0.4-0.7 kHz, for pout 0.1-0.25 kHz, for horse mackerel 0.1-2 kHz and for Atlantic herring 4 kHz. For cod, pollack and eel, no 50% reaction thresholds were reached. Reaction threshold levels increased from similar to 100 dB (re 1 mu Pa, rms) at 0.1 kHz to similar to 160 dB at 0.7 kHz. The 50% reaction thresholds did not run parallel to the hearing curves. This shows that fish species react very differently to sound, and that generalisations about the effects of sound on fish should be made with care. As well as on the spectrum and level of anthropogenic sounds, the reactions of fish probably depend on the context (e.g. location, temperature, physiological state, age, body size, and school size).
    Effect of satiety on brain activation during chocolate tasting in men and women
    Smeets, P.A.M. ; Graaf, C. de; Stafleu, A. ; Osch, M.J.P. ; Nievelstein, R.A.J. ; Grond, J. van der - \ 2006
    American Journal of Clinical Nutrition 83 (2006)6. - ISSN 0002-9165 - p. 1297 - 1305.
    human orbitofrontal cortex - sensory-specific satiety - gender-differences - liquid food - eating behavior - sex-differences - stimuli - appetite - humans - fmri
    Background:The brain plays a crucial role in the decision to eat, integrating multiple hormonal and neural signals. A key factor controlling food intake is selective satiety, ie, the phenomenon that the motivation to eat more of a food decreases more than does the motivation to eat foods not eaten. Objective:We investigated the effect of satiation with chocolate on the brain activation associated with chocolate taste in men and women. Design:Twelve men and 12 women participated. Subjects fasted overnight and were scanned by use of functional magnetic resonance imaging while tasting chocolate milk, before and after eating chocolate until they were satiated. Results:In men, chocolate satiation was associated with increased taste activation in the ventral striatum, insula, and orbitofrontal and medial orbitofrontal cortex and with decreased taste activation in somatosensory areas. Women showed increased taste activation in the precentral gyrus, superior temporal gyrus, and putamen and decreased taste activation in the hypothalamus and amygdala. Sex differences in the effect of chocolate satiation were found in the hypothalamus, ventral striatum, and medial prefrontal cortex (all P <0.005). Conclusions:Our results indicate that men and women differ in their response to satiation and suggest that the regulation of food intake by the brain may vary between the sexes. Therefore, sex differences are a covariate of interest in studies of the brain's responses to food.
    Boar Contact does not Induce Oxytocin Release During the Period of Embryo Migration in Sows
    Langendijk, P. ; Schams, D. ; Soede, N. ; Kemp, B. - \ 2006
    Reproduction in Domestic Animals 41 (2006)3. - ISSN 0936-6768 - p. 238 - 240.
    uterine activity - lactating sows - estrous sows - pig - radioimmunoassay - pregnancy - prolactin - behavior - stimuli - cattle
    Nine multiparous cyclic sows with permanent jugular catheters were introduced to a boar at day 10 (n = 9) or 11 (n 5) after ovulation to study the effect on oxytocin (OT) release. If it occurs, the release of OT might play a role in embryo migration which occurs around this time, by stimulating uterine contractions. Blood samples were taken before introduction of the boar and at 2-min intervals up to 10 min after boar introduction. On average, OT levels after boar introduction were not higher than before. In only three out of the 14 occasions of boar introduction, a rise in OT level was observed that was higher than two times the standard deviation above base level. However, even on these occasions OT levels were far below the range normally observed during other events where exogenous stimuli cause OT release, such as boar introduction during estrus and suckling during lactation. We conclude that boar contact around day 10 of the estrous cycle does not induce a biologically significant OT release in sows.
    Attraction of the amphipod Gammarus pulex to water-borne cues of food
    Lange, H.J. de; Lürling, M.F.L.L.W. ; Borne, J.J.G.C. van den; Peeters, E.T.H.M. - \ 2005
    Hydrobiologia 544 (2005)1. - ISSN 0018-8158 - p. 19 - 25.
    released chemical cues - asellus-aquaticus - crustacea - growth - conspecifics - predators - stimuli - minus - diet - pseudolimnaeus
    We examined the ability of the amphipod Gammarus pulex to detect chemical cues released from potential food sources. Therefore, response of G. pulex to chemical cues from food was tested in paired-choice laboratory experiments. Comparisons were made between artificial and natural leaves, with and without the importance of aufwuchs, and with different components of the aufwuchs community. Our study demonstrated that G. pulex actively chose its food and that G. pulex is most strongly attracted to the aufwuchs on discs rather than to the leaf itself. Fungi and bacteria are more important in the food selection process than algae probably because fungal and bacterial cues are more specific cues for decaying leaves than algal cues, since algae also grow on mineral substrates and then do not contribute to leaf decomposition
    The effect of an audience on the gakel-call and other frustration behaviours in the laying hen (Gallus gallus domesticus)
    Zimmerman, P.H. ; Lundberg, A. ; Keeling, L.J. ; Koene, P. - \ 2003
    Animal Welfare 12 (2003)3. - ISSN 0962-7286 - p. 315 - 326.
    male chickens - human-beings - fowl - stimuli - courtship - fear
    When thwarted in a behaviour, laying hens show an increase in stereotyped pacing, displacement preening and a specific vocalisation known as the 'gakel-call'. How these behaviours, which might serve as indicators of welfare, are influenced by social factors is not yet known. In this study, we investigated the effect of an audience (another bird or a human) on the expression of the gakel-call and other behaviours indicating frustration. Twenty-four Lohman Brown hens were trained to gain free access to food in a test cage. Sixteen hens were used as test birds and eight as non-test audience birds. The food-deprived test hens were tested for 15 min in a non-thwarting situation (food freely available) and for 15 min in a thwarting situation (food covered but visible). For both situations we investigated four different treatments: no audience in the adjacent cage; a non-thwarted audience bird in the adjacent cage; a thwarted audience bird in the adjacent cage; and finally a human audience. The durations of stereotyped pacing and displacement preening were significantly higher in test birds during thwarting than during non-thwarting; thwarted birds also gave significantly more gakel-calls compared to non-thwarted birds. The test birds, and also the audience birds, gave more gakel-calls when thwarted in the presence of a thwarted conspecific than when in the presence of a non-thwarted bird, but there were no significant differences in stereotyped pacing or displacement preening, which are usually associated with frustration. In conclusion, this study supports the view that the gakel-call signals frustration in laying hens. Furthermore, the state of the audience influences the occurrence of gakel-calls in thwarted hens. Thus, when using the gakel-call as a welfare-indicator, the social aspects of the vocal expression of frustration in laying hens should not be overlooked
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