P E R T E M U A N 4

A Y U R I A N A S A R I , M . S I , P S I

PERSEPSI VISUAL

Tujuan instruksional :

Setelah pertemuan ini mahasiswa mampu memahami dan menjelaskan mengenai :

1. Proses informasi penglihatan

2. Persepsi visual

3. Ilusi penglihatan

CAHAYA

DIMENSI CAHAYA

PANJANG GELOMBANG: warna (hue)

TINGGI GELOMBANG : kecerahan (brightness)

GABUNGAN PANJANG GELOMBANG : saturasi

COLOR VISION

Properties of color

Hue warna

Saturation gabungan warna

Brightness terang mendekatnya warna ke putih

WARNA

SUBSTRAKSI WARNA

Jika tiga warna utama

dicampurkan (pigmen),

maka panjang

gelombang berkurang

shg menghasilkan hitam.

PENAMBAHAN WARNA

Jika tiga warna utama

dicampurkan (cahaya),

maka panjang

gelombang bertambah

dan menghasilkan

warna putih.

STRUKTUR MATA

STRUKTUR MATA

Pupil- adjustable opening in the center of the eye

Iris- a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil opening

Cornea and Lens- clear membrane and transparent yet flexible disc shapes behind pupil that bending and changes shape to focus images on the retina

STRUKTUR MATA

Retina inner surface of eye

light sensitive

contains rods and cones

layers of neurons

beginning of visual information processing

The most important part of the retina is the fovea, a tiny area in the center of the retina at which vision is at its best

The multilayered light-sensitive surface in the eye that records electromagnetic energy and

converts it to neural impulses for processing in the

brain.

has approximately 126 million receptor cells.

two kinds of visual receptor cells: rods and cones.

Transduksi

RETINA

KARAKTERISTIK RODS DAN CONES

SEL BATANG (RODS) SEL KERUCUT (CONES)

= 120 juta

Melihat hitam dan putih

Berfungsi pada cahaya redup

Bentuknya kurus dan panjang

Tidak ada di fovea

= 6 juta Melihat warna Berfungsi pada cahaya

terang

Bentuknya gemuk dan pendek

Berada di fovea dan di luar fovea

SENSASI PENGLIHATAN

Bipolar cells Receive input

from receptor cells

Ganglion cells Receive input

from bipolar cells

Blind spot Area where

axons of ganglion cells leave the eye

ADAPTASI

Dark adaptation Increased sensitivity of rods and cones in darkness

Light adaptation Decreased sensitivity of rods and cones in bright light

Afterimage Sense experience that occurs after a visual stimulus has

been removed

VISUAL INFORMATION PROCESSING

Optic nerve Made up of axons

of ganglion cells

carries neural messages from each eye to brain

Optic chiasm Point where part of

each optic nerve crosses to the other side of the brain

VISUAL INFORMATION PROCESSING

Parallel processing : the simultaneous distribution of information across different

neural pathways

Binding , the bringing together and integration of what is processed by different

pathways or cells

PERSEPSI VISUAL - PROSES PARAREL

Pada persepsi visual, orang harus menyadari apa yang dilihat dan dimana letaknya, untuk dapat berespon dengan tepat.

What pathway terletak di lobus temporal, memproses informasi mengenai apa benda tersebut termasuk warna, bentuk dan tekstur. Mis : mengenali wajah.

Where pathway terletak di lobus parietal, berkaitan dengan proses informasi pergerakan dan kedalaman benda. Mis : untuk menyeberang jalan.

Juga terdapat di pendengaran dan perabaan.

VISUAL CORTEX

Most visual information travels to the primary visual cortex, where it is processed, before moving to other visual areas for further analysis (Schira & others, 2010).

Feature detectors are neurons in the brains visual system that respond to particular features of a stimulus.

DETEKSI BENTUK

Pada lobus temporal terjadi kombinasi aktifitas ketika

seseorang melihat suatu benda.

Teori penglihatan warna

1. Trichromatic theory

Thomas Young (1802) & Hermann von Helmholtz (1852)

= color perception is produced by three types of cone

receptors in the retina that are particularly sensitive to

different, but overlapping, ranges of wavelengths.

cones sensitive to red, blue, and green.

Color blindness The nature of color blindness depends on which of the

three kinds of cones (red, blue, or green) is inoperative

(Machado, Oliveira, & Fernandes, 2009).

BUTA WARNA

Approximately 10% of men and 1% of women

have some form of

colorblindness

Dichromats

People who are blind to either red-green or blue-

yellow

Monochromats

People who see no color at all, only shades of light and dark

Orang yg buta merah-hijau bermasalah dalam melihat angka di gambar

Ewald Hering -- Teori trikromat tidak dapat menjelaskan semua penglihatan warna dan

color after-image

Orang dengan penglihatan normal tidak dapat melihat merah kehijauan atau biru kekuningan

TEORI PENGLIHATAN WARNA

2. Opponent process theory

Ewald Hering (1878)

= states that cells in the visual system respond

to red-green and blue-yellow colors; a given

cell might be excited by red and inhibited by

green, whereas another cell might be excited

by yellow and inhibited by blue.

1. PERSEPSI BENTUK (SHAPE)

2. PERSEPSI KEDALAMAN (DEPTH)

3. PERSEPSI GERAK (MOTION)

4. KONSTANSI (CONSTANCY)

PERSEPSI VISUAL

PERSEPSI BENTUK

Contour : a location at which a sudden change of brightness occurs

gestalt psychology is a school of thought interested in how people naturally organize their perceptions

according to certain patterns.

main principle :

the whole is different from the sum of its parts.

GESTALT LAWS

1. Closure

2. Figure and ground

3. Proximity

4. Similarity

5. Continuation

Depth perception is the ability to perceive objects three-dimensionally.

1. BINOCULAR CUES

= depth cues that depend on the combination of the images in the left and right eyes and on the way the two eyes work together.

- Retinal disparity adalah perbedaan dalam bayangan-bayangan yang jatuh pada retina dari kedua mata

Convergence -- A binocular cue to depth and distance in which the muscle movements in our two eyes provide information about how deep and/or far away something is.

2. MONOCULAR CUES

= depth cues available from the image in one eye, either the right or the left.

PERSEPSI KEDALAMAN

1. Familiar Size

2. Height in the field of view

3. Linear perspective

4. Overlap (superposition)

5. Shading

6. Texture gradient

MONOCULAR CUES (PICTORIAL CUES)

Familiar size : Isyarat kedalaman dan jarak didasarkan pada pengalaman kita

mengenai ukuran standar dari objek.

Misalnya : kita memiliki pengetahuan

mengenai ukuran jeruk, sehingga kita bisa

memperkirakan berapa jauh jarak jeruk

berdasarkan ukuran citranya di retina.

Height in field of view :

objek yang

lebih tinggi di

dalam suatu

citra dihayati

sebagai

objek yang

lebih jauh.

Over lap (Superposition) Jika suatu objek

diletakkan sedemikian

rupa sehingga

menghalangi pandangan

objek lain, orang

menghayati objek yang

menutup sebagai lebih

dekat.

Gradient of texture : struktur gambar semakin halus bila jarak semakin jauh

Linear perspective :

Jika garis pararel tampak bergabung, mereka dihayati seakan-akan menghilang di kejauhan.

Deteksi gerakan :

1. Terdapat neuron khusus yg mendeteksi gerakan

2. Feedback dari badan

3. Informasi dari lingkungan

Gerakan :

1. Real movement

2. Apparent movement

PERSEPSI GERAK

PERGERAKAN APPARENT

Muncul saat objek dalam kondisi diam, namun kita mempersepsikannya bergerak.

Terdapat dua bentuk, yaitu :

1. Stroboscopic motion, yaitu ilusi pergerakan yang diciptakan melalui stimulasi yang terus menerus pada bagian-bagian yang berbeda di retina. Misalnya : film kartun

2. Movement aftereffects, terjadi ketika kita melihat gerakan yang terus menerus kemudian melihat ke permukaan lain, terlihat bergerak dengan arah yang berlawanan.

INDUCED MOTION

Misalnya :

- Melihat bulan di langit cerah dengan melihat bulan diiringi awan-awan yang bergerak.

- Saat naik mobil, kemudian kendaraan di samping kita bergerak, kita merasa bahwa kita yang bergerak.

= the recognition that objects are constant and unchanging even though sensory input about them is changing.

Size constancy is the recognition that an object remains the same size even though the retinal image of the object changes

Shape constancy is the recognition that an object retains the same shape even though its orientation to you changes.

Color constancy is the recognition that an object retains the same color even though different amounts of light fall on it.

KONSTANSI PERSEPSI

Ilusi visual muncul ketika ada perbedaan antara

kenyataan dan representasi visualnya.

Salah mengartikan isyarat untuk mempertahankan

konstansi.

ILUSI VISUAL