Psych 311 - Psychophysical Development

OUTLINES

Chapter 6

Early Stimulation

Rev. 1/23/03

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I. Introduction

A. Manipulation of a young animal’s environment

1. providing infants with restricted periods of supplemental stimulation (handling)

2. environmental enrichment- augmented levels of stimulation

3. sensory/perceptual programming- exposure to specific stimuli

II. Handling

A. Bernstein (1952)

1. petted rats for 10 min every day then tested in a T maze with food reinforcement

2. handled subjects required fewer trials to master maze and made less errors

B. Weininger (1956)

1. 10 min of stroking from days 21 to 42

2. effects: larger size of rats, greater skeletal strength, less affected by stress, and more active than non-handled

C. Conclusions

1. handling before weaning is much more effective than its administration before weaning

D. Physiological Effects of Handling

1. Morton, Denenberg, and Zarrow (1963)

a. handled rats of both sexes exhibit earlier sexual maturation

b. handling advances the time at which levels of brain cholesterol rise

c. earlier release of corticosterone from adrenal gland in handled rats

d. promotes physical well-being

2. Levine and Otis

a. fewer moralities among handled rats in response to 120 hours of food and water deprivation

b. enhanced resistance to cancer

3. Altman, Das, and Anderson

a. handling alters central nervous system

b. injected handled and controlled rats on day 11 with thymidine- a precursor of DNA

c. higher rate of mitosis in cerebellum, hippocampus, and neocortex of handled subjects

4. Denenberg, Garbanati, Sherman, Yutzey, and Kaplan

a. ablation of the right neocortex affected the activity of handled males (Induction of lateralization)

5. Wilson, Willner, Kurz, and Nakel

a. handled rats, removed from mother, placed in a box, and shaken gently for 5 min

b. on days 9, 11, and 13 removed from box and left undisturbed

c. handled rats exhibited greater potentiation than controls as seen from electrophysiological recordings (application of electrical stimulation to the hippocampal cells 30 min after the initial application of a brief and intense electrical stimulus)

E. Behavioral Effects of Handling

1. Two Major Behavioral Outcomes of Handling

a. Handling influences organisms reactivity to stressful stimuli (emotionality). Reactivity often assessed by amount of activity displayed in a novel environment.

1) Inverse relation exists between such activity and emotionality as rodents tend to freeze when they are frightened.

2) Handling effects an animal’s ability to acquire new behaviors.

b. Emotionality

1) Dennenberg and Morton (1962) found adult rats handled daily from birth to weaning to be less emotional than the controls.

a) Also indicative of reduced emotionality was a decline in defecation.

b) Handling need not be performed through entire lactation for emotionality to be affected.

2) Dennenberg, Morton, Klein and Grota (1962) reported that handling from birth to daytime is sufficient. The greater amount of early stimulation, the greater the attenuation of emotionality.

a) Rats are now only species in which handling reduces emotionality also rabbits and other rodents.

3) Meyer and McCormick (1978) placed handled and non-handled mice into an apparatus in which different levels of electric shock were administered through the grid floor.

a) Reactivity to shock assessed by recording number of times jumping, running and squeaking.

b) Handled mice reacted to shock less intensely than non-handled subjects.

4) Levine (1962) provided evidence linking handling to a modification to the pituitary/adrenal system handled and non-handled rats were observed were administered electric shock.

a) Blood samples were taken for Corticosteron (CCT) analysis from separate groups of animals at separate times following shock termination.

5) Handling affected rapidity with which cortizone levels rose. Manipulated subjects exhibited a significant elevation as early as 15 seconds after termination. Controls show comparable rise until 300 seconds after shock.

a) Similar results found that whereas handled animals had a greater level of CCT and plasma when measured at the time of shock offset so handled animals appear to recover from stress faster than non-handled animals.

6) Levine (1967) found that handling attenuates pituitary/adrenal reactivity to the stress engendered in a novel environment.

a) Early handling facilitates rats later adaptation to stress.

b) Adrenal gland contains a finite amount of CCT that poses threat to animals while being also to the animal’s advantage to quickly secrete large amounts of CCT when faced with a life-threatening situation.

7) Meaney (1985) examined ability of handled animals to recover quickly from stress – shown by rapid return of CCT to baseline levels.

a) Reduction of adrenal CCT secretion is accomplished through a negative feedback system.

b) High levels of ACTH cause CCT release the ensuing elevated levels of CCT inhibit the release of additional ACTH.

c) Meaney assessed the degree to which CCT binds to various areas of the brains of handled and non-handled adult rats.

d) Handled animals may recover from stress with greater rapidity than non-handled animals because handling promotes development of CCT receptor system.

8) Meaney, Aitken, can Berkel, Bhatnogar and Sapolsky (1988) said enhanced negative feedback between CCT and ACTH has ramifications later in life.

a) Handled recover faster and have lower basal levels of CCT than controls.

b) Do no exhibit neuronal loss in the hippocampus or cognitive deficits seen in elderly rats.

c) Meaney concluded that handling prevents certain age-associated impairments.

c. Acquired Behavior

1) Daly (1973) reviewed that some studies have reported that handling facilitates avoidance conditioning and others report that it produced no effect.

a) Handling has been found to retard avoidance conditioning.

b) Improved performance may be secondary to a reduction of emotionality.

2) Weiner, Schnobel, Cubow and Feldon (1985) examined influence of handling on conditioning devoid of an aversive component and a positive component.

a) Accomplished with a latent inhibition paradigm in which repeated stimuli not followed by reinforcing consequences renders them incapable of future conditioning – causes subjects to learn to ignore stimuli.

b) Differences between handled and non-handled animals cannot be attributed to motivation – emotional differences, but to differences in attentional processes underlying learning to ignore irrelevant stimuli.

3) Rats were exposed to tones – later served as the conditioned stimulus in avoidance conditioning.

a) Both handled and non-handled females exhibited latent inhibition – only the handled males exhibited it.

b) Handling does affect at least one conditioning task that does not involve emotional – motivational component and does so only in the male - in this case handling produces a deleterious effect.

F. Handling as a Stressor - Two lines of Evidence support this

1. Denenberg, Haltmeyer, and Brumaghin (1967)

a. Handling and other manipulations that are unambiguously stressful exert similar effects on the infants

1) 2 day old rats

2) Application of various stressors, such as cold, heat, and electrical shock as well as handling

b. The release of corticosterone by handling not only is used to argue that handling is a stressor but it provides that basis for an explanation of how handling operates to affect later reactivity to stress

2. Deneberg and Zarrow (1970)

a. The sex hormones, which are also steroids are known to have their organizing effects during early infancy or even pre-natally

b. Corticosterone released from the adrenal gland must be localizing itself in the hypothalamic region

c. Handling is stressful in that it and unequivocal stressors yield similar developmental effects

3. Levine, Chevalier, and Korchin (1956)

a. Used 3 groups of rats

1) 1^st group received electrical shock

2) 2^nd group was handled

3) 3^rd group was left alone

b. Found that the avoidance performance of both the shocked and handled animals surpassed that of undisturbed animals

4. Deneberg and Smith (1963)

a. Reported that both the shocked and handled animals displayed increased open field activity

5. Ader (1969)

a. Found that handling and shock advance the age at which the 24 hour adrenocortical rhythm appear at first

6. Werboff and Havlena (1963)

a. 3 day old rats in 3 conditions

1) Microwave diathermy

2) Handling

3) Left alone

b. At 30 days rats were tested for seizure activity induced by exposure to sound

c. Found: 41% of undisturbed rats exhibited seizures

1) None of the handled or convulsed rats exhibited seizures

7. Landauer and Whiting (1964)

a. Controlled experiment studying early stress and stature

1) 278 Kenyan Children

a) Some vaccinated before 2 years of age, some after

b) Data collected ages 3-7 years of age

2) Found those vaccinated before age of 2 had grown more during the intervening years

3) Differences were found in height, leg length, and head circumference

4) Work provides evidence linking early stress to the enhancement of physical growth in males and females and to the acceleration of puberty in females

G. Premature Infants

1. Will extra stimulation benefit the premature infant?

a. Premature infants spend time in an incubator, which may make additional stimulation compensatory instead of supplementary.

2. Tactile Stimulation

a. Solkoff, Yaffe, Weintraub and Blasé (1969)

1) Five premature infants were given five minutes of stimulation per hour every hour for the first ten days. They were rubbed on their neck, back and arms.

2) Five other infants served as a control group who were only touched for feeding and changing.

a) Experimental infants were more active

b) 7-8 months later the infants were given the Bayley Test of Mental and Motor Development and those who were premature with stimulation were more active and physically healthy.

b. Scafidi et al (1986)

1) 20 premature infants provided with 3 15-minute sessions a day for 10 days.

a) Stimulated infants gained 47% weight per day than the controls did.

b) They were also discharged 6 days earlier than the controls.

c. Kuhn et al (1991)

1) Tactile stimulation increases levels of norepinephrine and epinephrine

2) Levels of dopamine, cortisol and growth hormone don’t differ from controls in experimental groups.

a) Suggests stimulation affects activity of sympathetic nervous system.

3. Vestibular Stimulation

a. Clark, Cordero, Goss and Manos (1989)

1) 15 premature infants put in a designed incubator that rocked side to side.

2) Rocked 15 minutes per day three times a week for two weeks.

a) Infants scored higher on the Dubowitz Neurological Assessment Test

b) Groups didn’t differ on habituation or weight gain.

4. Combination of Stimulation

a. Scarr-Salapatek and Williams (1973)

1) Gave a combination of visual, tactile and vestibular stimulation to 15 pre-term infants during a 6-week stay in the hospital.

2) Trained the mother’s to maintain higher levels of stimulation.

a) Experimentals showed increase development status than the controls at 4 weeks.

5. Treatment after Release from the Hospital

a. Rice (1977)

1) Mother’s were trained to give a combination of stroking and rocking/cuddling to infants for 30 days following the release from the hospital.

a) Showed they exceeded controls in neurological and mental development assessed by the Baley Scales.

6. Issues Related to Handling and Development

a. Stimulation produces beneficial effects.

b. Parents might augment effectiveness of handling regimen.

c. The endurance of the handling phenomenon.

1) How long does the effect of supplementary stimulation last?

d. Does supplement stimulation benefit full term infants:

1) Clark, Kreutzberg and Chee (1977)

a) 13 infants were exposed to vestibular stimulation by spinning in a rotating chair.

(1) It was suggested that tit may promote the maturation of the vestibular reflex.

III. Environmental Enrichment

A. The increased stimulation in an enriched environment enhances brain activity which manifests in physiological and behavioral change

1. differences between brains and behavior of subjects from enriched and impoverished environments should be apparent

2. Hebb

a. proposed enriched experiences early in life lead to alterations of brain and improvement in problem-solving

B. What is really being studied

1. environmental enrichment research

a. study impact of living in an environment providing enhanced levels of stimulation

b. enriched environment compared to impoverished env’t

c.. however, animals don’t live in impoverished env’t

d. the enriched env’t should be considered the control and impoverished the experimental condition

C. Environmental Enrichment and Problem Solving Behavior

1. Hebb

a. rats as pets with much of the time spent outside the cage had enhanced problem-solving abilities

b. first demonstration of effects of enrichment on learned beahavior

2. Forgays and Forgays

a. rats raised in groups in large cages with play things made fewer errors in Hebb –Williams maze than animals kept in similar cages without play things

b. the latter condition (animals kept in large cages without play things) was superior to animals kept in small cages with or without play things

c. both cage size and stimulus objects are influential

3. Forgays and Read

a. rats exhibit a period of maximum sensitivity to enrichment

b. enrichment commencing immediately after weaning is more effective than enrichment from birth to weaning

1) the latter did not differ from those given no enrichment

4. Assessment

a. Hebb-Wiliams maze

b. Lashley III maze

c. 17-unit radial arm maze

d. environment enrichment leads to increased performance

5. Wilson, Warren, and Abbott

a. enlarged version of Heb-Williams maze

b. cats placed in large room with other cats, toys, for 5 hours a day from days 46 to 90 made less errors than controls

6. Mogensen

a. enriched animals exhibit enhanced performance on delayed alternation task

b. environment enrichment may bias the rat towards applications of spatial hypotheses during problem solving behavior

7. Brown/Forgays and Forgays

a. rats kept in enriched environment are more disrupted by rotation of the maze than nonenriched subjects

b. this means that this increased performance may be due to the fact they make better use of extra maze cues – such as position of overhead lamp

8. When can’t the 2 groups be differentiated?

a. simple tasks: visual

b. acquired taste aversions

c. active avoidance

d. conditioned heart rate suppression

D. Environmental Enrichment of the Brain - Size

1. Bennett and gang

a. placed 25 day old rats in enriched or standard setting

b. 30 days later killed and removed brains

c. separated occipital and somesthetic cortices

d. these and the dorsal cortices of enriched rats were significantly heavier

e. greatest effect in occipital cortex

1) serves other functions

f. animals housed singly in wire cage within enriched env’t do not have altered cerebral weights

g. effects of env’t enrichment not permanent

2. Bennett and gang again

a. increase in occipital cortex weight no longer apparent 32 days after rats from enriched env’t are housed under standard setting

3. Similar effects also found in other species

4. Walsh

a. cerebral cortex also gets longer

1) 30 days of exposure – 1.2% longer than control

2) 80 days – 2.5% longer

3) graded effects

4) cortical thickness also increases as function of enrichment

a) greatest effect in occipital cortex

5. Another Difference

a. occipital cortices of enriched rats contain more glial cells

b. occipital cortex of enriched rat and cat comprise larger area than controls

E. Neuroanatomy

1. Holloway (1966)

a. Provided preliminary evidence linking environmental enrichment to neuroanatomical changes, to alter dendrite branching.

b. After 95 days in the enriched environment rats exhibit higher levels of dendritic branching in the occipital cortex.

c. Later confirmed by Volkmar and Greennough who reported the largest effects are seen in busel rather then apical dendrites

2. Beaulieu and Colonnier (1987)

a. Reported that the number of synapses associated with flat synaptic vesicles differ between enriched and controlled cats.

b. May be related to the fact that electrical activity of cortical neurons in response to certain visual stimuli are altered by environment enrichment.

3. Not all cell types within a particular cortical region exhibit dendritic plasticity and not all animals exhibit the same degree of plasticity.

a. Juraska (1984) reported that female rats manifest a smaller degree of branching then males. An assessment of the influence of androgen would be of interest here.

b. Dendrite plasticity is not restricted to cells of the occipital cortex.

4. Greenough, Volkman, and Juraska (1973)

a. After 30 days of enrichment exposure increased branching is seen in rat temporal cortex.

b. For the monkey, enrichment affects only the motor cortex.

c. Plasticity is not even restricted to cortical tissue.

d. Reported that a noncortical structure, the cerebellum, also undergoes changes, including enhanced dendrite branching, as a consequence of enrichment experience.

5. Volkmar and Greenough (1972)

a. Proposed that “the increased branching presumably provides increased surface for synaptic contacts and this potential of interneuronal interaction suggests a greater capacity for information processing, in the brain of the animal reared in a more stimulation environment.

6. Turner and Greenough (1985)

a. Using electron micrograph, found an increase of approx, 20% in the number of synapses per neuron in occipital cortices of enriched rats.

F. Neurochemistry

1. Attempts have been made to determine if neurochemical changes occur as a consequence of environmental enrichment, involving neurotransmitters.

a. If the brain of animals exposed to an enriched environment are more active, greater levels of a neurotransmitter such as acetylcnoline should be present as well as the enzyme required to break down the transmitter (acetylcholinesterase- ACHE)

2. Rosenzwieg, Bennett-Diamond (1972)

a. Only a trend exists in the direction of a greater absolute level of ACHE activity in both the cortex and sub cortex of enriched rats

b. Because the cortex of enriched animals is larger, ACHE should be expressed as a function of unit weight

c. When this is used the activity of the enzyme is slightly lower in the cortex and higher in the sub cortex.

d. Data relating to other neurotransmitters are inconclusive.

3. Because protein synthesis had been implicated in information processing and because the enrichment environment has been thought of as providing more stimuli of info to process, quantitative and qualitative differences in brain protein synthesis have been predicted.

G. Application of Environmental Enrichment

1. May have therapeutic applications

a. Enriched environments have been shown to attenuate behavioral deficits caused by damage to certain regions of the brain.

b. Will, Rosenzweig, Bennett, Hebert, and Morimoto

1) Show that enrichment ameliorates the adverse affects of occipital cortex lesions on performance in Hebb-Williams maze.

2) 2 hrs. a day of enrichment exposure for 60 days reduces number of errors.

3) Also fascinating, Performance of a complex motor task following lesions of motor cortex and conditioning following damage to the dorsal hippocampus.

4) Enrichment facilitates maze learning and retention in brain damaged by the prenatal induction of hypothyroidism and by prenatal administration of monosodium glutamate.

c. Only damage to particular brain structures is ameliorated by environment, damage to septum, endocrinal cortex, of fimbria- fornix is not affected.

d. Enrichment also appears to contract some of the deficits associated with aging.

1) Enrichment retains its ability to alter the brain even when subject is elderly.

e. Cummlins

1) Reported an increased in whole brain weight.

f. Brain changes in old animals are of a lesser magnitude then those in younger animals.

1) Enrichment provides some protection against age-related behavioral decline.

H. What causes the enrichment phenomenon?

1. Three major hypotheses

a. Environmental enrichment causes alterations in hormone levels, which act on the brain

1) Hormones produced by the thyroid, pituitary and goads are involved in brain

b. Effects observed in differential housing experiments essentially are caused by the control condition rather then by the environment

1) Control condition is so abnormal that it creates a state of chronic stress

2) Certain stress-related hormones adversely affect brain development

c. Differences between enriched and impoverished animals are caused by the fact that enriched have greater opportunity to store information about environment

1) May result in brain changes associated with formation of synapses

2. Stress Hypothesis

a. If the stress engendered by the control condition causes retardation of brain development it must be demonstrated that control subjects are consistently more stressed and enriched subjects

1) Does not appear that animals housed under impoverished conditions are subject to chronic stress

IV. Sensory/perceptual programming-allows young organism to experience only specific stimulation

A. Visual stimulation

1. Individual neurons of the visual system, specifically cells of the lateral geniculate nucleus and that portion of the visual cortex are selectively activated by certain features of a visual stimulus

2. The pattern of retinal stimulation that activates a cell is called the cell’s receptive field

a. Kuffler (1953) showed that the receptive fields of ganglion cells have concentric “on” and “off” regions

1) Spot of light falling on the “on” region of the retina increases the firing rate of the cell

2) Stimulation to the surrounding “off” region inhibits cell’s activities

3. Hubel and Wiesel (1959)-identified 3 classes of cells of the cat striate cortex that differ in terms of receptive field

a. Simple cells respond to a feature such as a line, bar or edge, having specific orientation

b. Complex cells are sensitive to the direction of motion and the location of the particular feature within the visual field in not critical

c. Hypercomplex cells exhibit the properties of complex cells, but in addition respond selectively to stimuli of particular lengths

4. Wiesel and Hubel (1963) examined the influence of early visual deprivation

a. Accompanied by preventing visual stimulation from reaching one eye of the kitten

1) Suturing the eyelid so it would not open at a time of eye opening or by severity restricting visual input with translucent goggles

2) Sutures/goggles were removed after 3 months and deprived and normal eye were examined

a) The few cells that could be activated by stimulating the deprived eye had abnormal receptive fields

5. Hirsch and Spirelli (1970)-initial discovery that early visual experience can modify receptive fields of cells in the striate cortex

a. 3 weeks of age-total visual experience of kittens consists of viewing receptive fields of cells

1) A white field containing 3 black vertical lines with one eye

2) A white field with 3 black horizontal lines with the other eye

b. Unlike normal kittens, the receptive fields of these kittens were oriented either horizontally or vertically

1) Cells with horizontal receptive fields were activated only by appropriately stimulating the eye that had been exposed to horizontal lines

2) Cells with vertical receptive fields responded only when the appropriate stimulus was given to the eye that had been exposed to vertical lines

6. Early visual stimulation reduces the # of stimuli that can activate particular striatal neurons, or in other words, the visual system in a sense has been simplified

a. Hirsch (1972) referred to such an early experience as “environmental surgery”

7. Muir and Mitchell (1973)

a. performed experiment designed expressly to assess the impact of early visual experience on later behavior

1) vertical lines vs. horizontal lines

a) 5 hours a day from day 20 to 4 months

b) trained to press panel with nose

(1) 1 panel was dark and blank

(2) 1 panel black parallel lines (grating)

c) cats were rewarded if they could distinguish the panel with grating

(1) found to be influenced by early experience

8. Freeman, Mitchell, Millodot (1972)

a. reported individuals suffering from astigmatism continue to exhibit differences in the resolution of vertical and horizontal grating even though vision was corrected with glasses

b. astigmatism is usually present from an early age

1) this defect produces a biasing similar to that produced by exposing young animals to vertical and horizontal lines

9. Annis and Frost (1975)

a. conducted study designed to determine whether individuals with normal visual activity are also influenced by selective early visual experience

1) one group of adult Euro-Canadians, who grew up with a visual environment with marked predominance of vertical and horizontal contours

2) another group of Cree Indians, raised in conditions with no predominating contours

b. subjects were presented a gradient of a fixed spatial frequency, rotated to one of four orientations

1) asked to adjust pointer to correspond to the orientation of the grating

c. assessed acuity by placing gradient at varying distances from the subject

1) Euro-Canadian sample varied; acuity was greater for vertical and horizontal gratings

2) Cree sample did not exhibit higher resolution for vertically and horizontally oriented gratings

d. Disparity between the 2 groups is caused by differing amounts of early visual exposure to vertical and horizontal contours

B. Olfactory Stimulation

1. Frazier and Brunjes (1988)

a. reported a 25% decrease in size of the olfactory bulb of 30 day old rats subjected to the surgical closure of one nostril on day 1 of life

b. animals exposed to a single intense olfactory stimulus do not exhibit altered acuity for that stimulus, although they may be deficient in the detection of other odors

2. Rossello-Austin and Williams (1990)

a. exposed rats from day 1 to 21 of life to different odors every 24 hours

1) odorants placed in bottles and suspended from cage tops

2) analysis on day 31 revealed that the olfactory bulbs of odor-exposed animals contained 35% more mitral cells and 40% more granue cells than those of nonexposed controls.

3) mitral cells of experimental subjects contained significantly larger nuclei

3. Leon et al

a. conducted series of experiments illustrating early olfactory experience does affect neuronal activity in response to the later presentation of a now familiar odor.

b. Coopersmith and Leon (1986) demonstrated that the enhanced activity of olfactory bulb cells caused by early olfactory experience persists in to adult life

4. To what extent does perineal stimulation presented in conjunction with the odor conjunction with the odor contribute to the enhancement of 2 DG uptake (2-deoxy-D glucose)?

a. Plays important role because there is no enhancement of 2 DG uptake when the familiar olfactory stimulus is presented with the tactile stimulus

5. Sullivan and Leon- even a single exposure to an odor on day 6 combined with tactile stimulation can enhance 2 DG uptake in response to odor even in the following day

a. Early olfactory experience alters neuronal activity of the olfactory system

1) Early exposure to an odor leads to later preference to odor

2) May not like it more but it maybe less aversive to the a novel odor

b. Research consisted of exposing young animals to artificial odorants for a lengthy period

1) If rats spend 1^st 14 days of life with mother or nest is scented it prefers to huddle with specifics that are similarly scented

a) Male rat pups were kept with mothers whose nipples and vaginal area had lemon

b) When tested around day 100 they ejaculated more quickly when presented with a female whose vaginal area was coated with lemon

c) Therefore for this mammal the degree to which a feminine feature is sexually arousing to adult males can be established in the context of suckling

c. Early olfactory experience also influences human odor preference

1) 12-18 day old infants presented with two gauze pads one with odor from mothers underarms and the other with odor from other adults

a) Breast feeding but not bottle-feeding infants preferred their mothers odor to those of others

b) Bottle fed infants does not show preference between mother’s odor and other female odor

c) Breast feeders spend more time in close proximity to mothers skin therefore with more experience with maternal odor

d. Balogh and Poiter exposed some 5.0 to 21.5 hour old infants to either cherry odors or ginger.

1) Females not males preferred familiar odor

2) Some preferences can develop after much briefer exposures

a) 10-15 day old male rats were exposed to lemon oil or methysalicyate for 3, 9 or 27 minutes

b) The ones with only 3 minute of exposure preferred the familiar odor

c) Preference still evident when tested 24 hours after the exposure period

e. In a test where rats were exposed to an odor for 10 minutes a day and later exposed to odors they spent more time near the first odor

1) Effect observed only for animals that received tactile stimulation with the presentation of the odor

2) Early olfactory experience produces brain and behavior changes

a) Brain changes are similar to those caused by early visual stimulation both involve the alteration of selective groups of neurons

b) Behaviorally visual experience shown to affect acuity whereas olfactory experience influences preference