Object Perception CLPS 0020 Introduction to Cognitive Science

Object Perception CLPS 0020: Introduction to Cognitive Science Trent Wirth Fall 2016

Why study Perception? Remember Marr’s levels of analysis? • Perception is the input to the cognitive system – Computational Level: If you don’t understand the input, you’re a little lost

What is object recognition? • Our world is filled with complex scenes BB-8 R 2 -D 2

A more common example You do this ALL THE TIME

A simple model of object recognition Retinal image Object description Stored object representations Identification

Questions • What are the nature of object description and stored object representation? • How are the mappings carried out?

Early models of object recognition • Template matching • A bucket • Feature matching • Letter between G and I T E C T • Work for barcodes (by computers), but don’t exactly translate to human perception

Two Contemporary Models • Object-centered approach – Perceptual image is broken down and contrasted against a stored representation • Viewer-centered approach – Perceptual image is contrasted against an object representation that is dependent on the viewer’s orientation

Object-centered approach (1) • Marr et al (1978): Generalized Cylinders/Cones

General Approach / Problems • Object representations are built from these “building blocks” • Perceptual image builds up to generalized cones and compares against stored representations • Might be a good strategy to get computers to recognize objects – But little psychological evidence

Object-centered approach (2) • Biederman’s (1987, 2000) Geon theory (aka. “Recognition by Components”)

Geon Model • Set of basic shapes that were the building blocks of all object representations – Number of basic shapes changed over the years (initially 5, now 32 of them) • Object recognition is performed by breaking down visual representation into geons and comparing combinations with object representation – The more geons you could view, the easier object recognition would be

Supporting evidence for Geon model (Biederman et al, 1973)

Thoughts on Geons • Geometric objects as building blocks – Intuitive! – more information = better recognition • Problems? – Very abstract – Where do these building blocks come from?

Contrast: Viewer-centered approach • Multiple views are stored for each object • One view is “Canonical” • Canonical views are faster to recognize • Transformational mechanism is required to compare perceptual image with object representation

Support for viewer-centered approach • Tarr (1995): Novel object learning • Two phases of experiment • Phase 1: Learn a novel object

Phase 2 • Classify new views of objects – Is this the same or different?

Predictions Difference in perspective

Tarr (1995) Data • Reaction time increased for categorizing object as the same in a linear fashion as difference

Thoughts • Studies of object recognition under multiple perspectives support the viewer-centered approach • Our brain probably has both kinds of representations – An Example: Faces (More on this in face recognition lecture)

Making sense from noise • What is it – Do you see the dog? • Once you see the dog, can you not see the dog? – Perceptual system makes sense of noise to form objects

Categorizing Sounds - Speech • Speech sounds can vary in a number of ways • One dimension along which consonants vary is Voice-Onset-Time (VOT) – /ba/ vs. /pa/ • Adults do not perceive all changes along this continuum equivalently – Hear categories of sounds

Categorical Speech Perception • Eimas (1973): Habituated Sucking Response • Play a particular sound categorized as /pa/ or /ba/ over and over again – Method: Sucking rate is equivalent to looking time. It increases then decreases – Then change the sound

Speech Categorization Data • Eimas et al. (1971): Distinction between /pa/ and /ba/ in 1 month-olds and newborns

Conclusions • Speech (phoneme) perception involves a great deal of noise – Different frequencies: pitches, loudnesses, amplitudes, but also levels of background noise, multiple sources, etc. • At birth (or at least by 1 mo), we are beginning to categorize those sounds into meaningful units – Basis of language learning?

Cue Combination • A final piece of the puzzle – https: //www. youtube. com/watch? v=Gl. N 8 v. Wm 3 m 0