Perceptual Development Dr. Kline FSU-PC Perceptual development is rapid!!! Perceptual abilities develop to adult-like or near-adult levels by the age of 6 months. In contrast, rarely do infants speak at 6 months, walk at 6 months, or can do fine-motor tasks at this time. Perceptual development may be launching pad for other aspects of development to occur (Sternberg). Why is perception so important?? It’s the beginning of all behavior & mental processing. You can produce movements, behaviors, or language if you don’t have the physical apparatus to respond to objects & events in your environment. We need to tie perceptions to actions (consequences of produced actions). What is a sensation? Usually refers to the physical stimulus in the environment (light, sound waves). We convert physical energy from the world into neural energy our brains can process. What is perception? Refers to how we interpret the stimulus information our nervous system takes in & processes. Does perception equal physical reality? What do you think??? Task of perception: 3-Fold 1. Attending – what in environment is interesting enough to examine in detail? 2. Identifying- can you determine what the stimulus “is” from past memory? 3. Locating – how far away & in what direction is the object or person from you? Sternberg’s example of the 3 tasks of perception. “If you are in an Asian jungle and a tiger is charging, you need to orient your attention toward the tiger, to identify it as a tiger, and to locate how far away it is so that you can decide whether to climb a tree, shoot a gun, or pray.” (p.93) Visual perception-the basics Light- which can be thought of as discrete particles (photons) or traveling waves. Human Visible Spectrum Humans can detect waves of energy traveling through space between 380 & 760 nanometers). Wavelengths outside this spectrum are undetectable to the human eye. Some organisms do detect wavelengths outside our visible spectrum. E.g., Rattlesnakes detect in infrared!; bees detect ultraviolet light. Electromagnetic Radiation What are the 2 properties of light that influence visual perception? 1. Wavelength is associated with our perception of color. 2. Intensity is associated with our perception of “brightness.” Reflectance of light Light is reflected off of the surface of objects & to the eye. Light energy is converted into neural energy & then processed by the brain. Visual Pathways 1. Geniculostriate pathway- optic chiasm----LGN---Primary Visual cortex **involved in pattern perception, color vision** 2. Tectopulvinar pathway- optic chiasm---superior colliculus---Lateral posterior pulvinar---PVC **detection of light; spatial orientation** Primary Visual Cortex Common methods for examining infant perception (visual, hearing, etc.)? 1. Preferential looking paradigm- infants will stare at objects or events they find interesting. E.g., an infant is presented with 2 faces: Mom’s face & a stranger’s face. The infants stare longer & more intently at Mom. We can infer that the infant perceives the difference between his or her mother’s face & a stranger’s face as well as a clear preference for Mommy. 2. Habituation paradigm- Infants more likely to stare at a novel object than a familiar one. E.g., An infant is presented with 2 blue squares for 20 trials. On the 21st trial, a red square is presented in place of one of the blue squares. The infant spends significantly more time staring at the red square than the existing blue square. We can infer that the infant must be perceive the difference in the two colors (red & blue) since the stimulus only differed on this one feature. Attending to Visual patterns Infants may initially stare at a novel object (attention-drawing)… But, will only continue to stare at it, if the object is meaningful (attention-holding). Cohen argues that while attention-drawing objects may be similar over the lifespan, attention-holding objects differ markedly with time. What initially gets our attention? We “attend” to novel stimuli in the environment (bright lights, sounds, flashers). This orienting response called the “orienting reflex,” is present from birth. Why is this adaptive?? Do we need higher brain regions (cortex) to “orient?” No!!! The presence of subcortical structures is enough to elicit orienting. Graham et al., used a habituation paradigm with speech sounds on an anencephalic infant (no cortex) & found the infant showed orienting reflex. Anencephalic infant’s heart rate showed large decreases from baseline after a speech sound was presented. Response habituated after 6 stimulus presentations. When scanning the environment, what do infants look for? Very young infants (1 mos.) scan the edges of objects. They love contrasts & ignore interiors. (e.g., outside views of face) Largely subcortical By 2 mos. Infants start focusing visual attention on the interior views of objects. (e.g., stare more at eyes & mouth of a face, than on hairline). More cortical with time What features of stimuli hold the infants’ attention? Infants seek a moderate level of arousal in the environment (avoiding too much or too little stimulation). Evidence: newborns given a choice among a dimly lit, moderately lit, or brightly lit object, tend to prefer the moderately lit object (Lewkowicz & Turkewitz, 1981). Visual acuity (fine-detailed vision) Newborns – detect changes in brightness, movement in visual field, & track moving objects. Visual acuity is assessed using a preference looking paradigm. If infants are presented with a uniform gray field & black & white stripes they prefer the stripes. By varying the distance between black & white stripes & having the infant compare this with the gray field you can assess the infants’ acuity. Babies’ can discriminate the higher spatial frequencies by 6 mos. Acuity is poor ( 20/200 to 20/800) in first couple of months of life. Images are blurry & must be very close to baby’s eyes to be detected. By 6 mos. Acuity is near adult-levels. Factors that increase acuity with age: Pupil size increases Density of cones in fovea changes; a birth these are spaced apart, but they migrate toward the fovea with time. Do infants see colors? Yes!!!! 3-month-old infants can perceive most colors (reds, blues, & greens). Evidence: Bornstein repeatedly presented 4-month-old infants with a specific wavelength until they habituated to it. He then presented one of 2 alternative wavelengths: (A) one color which looked like a different shade of the same wavelength and (B) the other color which looked a different color than the original. Infants preferred looking B. Do infants see in 3-D? Infant depth perception improves with experience, which is necessary for proper brain development. 3-5 mos.–infants can coordinate their two eyes & begin seeing depth as adults do using stereoscopic vision (Birch, 1993;Mohn & van Hof-van Duin, 1986). Gibson & Walk (1960): Visual Cliff Study Babies placed on elevated glass platform with a decorative pattern directly beneath the glass on one side (the “shallow side”) & the same pattern several feet below the glass on the other side (the “deep side”). 6- 14 month-olds would not cross the “deep” side to get to their mothers even when encouraged to do so. Infants viewing preferences: 1. Human faces to other stimuli. 2. Mother’s face to other faces. 3. Attractive faces to non-attractive faces. Audition: Infants –well developed auditory systems, even before birth. Infants don’t hear better than adults. Sounds need to be louder (10-17 dB) for infants to hear them. Infants hear high frequencies quite well (they are poor at detecting low frequencies) & prefer to hear high-pitched voices. What do infants prefer hearing? Musical sounds over non-musical sounds (infants alter sucking patterns to hear musical sounds over noise) High-pitched voices (Mother) vs. low- pitched voices. Olfaction: Newborns produced “smiles” to strawberry & banana odors & grimaces/ cries to rotten- egg & fish odors (Steiner, 1979). Infants learn to prefer their mother’s scent to other women. Tactile Infants are very responsive to touch, like to be stroked and cuddled. Premature infants have better health outcomes (more likely to survive), if held & stroked regularly. Taste: Newborns respond to all four taste sensations. Rosenstein & Oster (1988) found that newborns produced distinct facial expressions in response to sweet, sour, bitter, & salty substances. Infants prefer sweet tastes (milk).