Let's read! We will often find out this sentence everywhere. When still being a kid, mom used to order us to always read, so did the teacher. Some books are fully read in a week and we need the obligation to support reading. What about now? Do you still love reading? Is reading only for you who have obligation? Absolutely not! We here offer you a new book enPDFd the perception of the visual world to read.

The Perception of the Visual World. By James J. Gibson. U.S.A.: Houghton Mifflin Company, 1950 (George Allen & Unwin, Ltd., London). Price 35s.

Visual attention: The past 25 years

This article examines the role of attention and automaticity in auditory processing as revealed by event-related potential (ERP) research. An ERP component called the mismatch negativity , generated by the brain's automatic response to changes in repetitive auditory input, reveals that physical features of auditory stimuli are fully processed whether or not they are attended. It also suggests that there exist precise neuronal representations of the physical features of recent auditory stimuli, perhaps the traces underlying acoustic sensory (“echoic”) memory. A mechanism of passive attention switching in response to changes in repetitive input is also implicated. Conscious perception of discrete acoustic stimuli might be mediated by some of the mechanisms underlying another ERP component (NI), one sensitive to stimulus onset and offset. Frequent passive attentional shifts might accountforthe effect cognitive psychologists describe as “the breakthrough of the unattended” (Broadbent 1982), that is, that even unattended stimuli may be semantically processed, without assuming automatic semantic processing or late selection in selective attention. The processing negativity supports the early-selection theory and may arise from a mechanism for selectively attending to stimuli defined by certain features. This stimulus selection occurs in the form ofa matching process in which each input is compared with the “attentional trace,” a voluntarily maintained representation of the task-relevant features of the stimulus to be attended. The attentional mechanism described might underlie the stimulus-set mode of attention proposed by Broadbent. Finally, a model of automatic and attentional processing in audition is proposed that is based mainly on the aforementioned ERP components and some other physiological measures.

The role of attention in auditory information processing as revealed by event-related potentials and other brain measures of cognitive function

Leptin is the primary signal through which the hypothalamus senses nutritional state and modulates food intake and energy balance1. Leptin reduces food intake by upregulating anorexigenic (appetite-reducing) neuropeptides, such as α-melanocyte-stimulating hormone2,3, and downregulating orexigenic (appetite-stimulating) factors, primarily neuropeptide Y4. Genetic defects in anorexigenic signalling, such as mutations in the melanocortin-4 (ref. 5) or leptin receptors6, cause obesity. However, alternative orexigenic pathways maintain food intake in mice deficient in neuropeptide Y7. CB1 cannabinoid receptors8 and the endocannabinoids anandamide and 2-arachidonoyl glycerol are present in the hypothalamus9, and marijuana10 and anandamide11,12 stimulate food intake. Here we show that following temporary food restriction, CB1 receptor knockout mice eat less than their wild-type littermates, and the CB1 antagonist SR141716A reduces food intake in wild-type but not knockout mice. Furthermore, defective leptin signalling is associated with elevated hypothalamic, but not cerebellar, levels of endocannabinoids in obese db/db and ob/ob mice and Zucker rats. Acute leptin treatment of normal rats and ob/ob mice reduces anandamide and 2-arachidonoyl glycerol in the hypothalamus. These findings indicate that endocannabinoids in the hypothalamus may tonically activate CB1 receptors to maintain food intake and form part of the neural circuitry regulated by leptin.

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Leptin-regulated endocannabinoids are involved in maintaining food intake

We perceive the shapes and material properties of objects quickly and reliably despite the complexity and objective ambiguities of natural images. Typical images are highly complex because they consist of many objects embedded in background clutter. Moreover, the image features of an object are extremely variable and ambiguous owing to the effects of projection, occlusion, background clutter, and illumination. The very success of everyday vision implies neural mechanisms, yet to be understood, that discount irrelevant information and organize ambiguous or noisy local image features into objects and surfaces. Recent work in Bayesian theories of visual perception has shown how complexity may be managed and ambiguity resolved through the task-dependent, probabilistic integration of prior object knowledge with image features.

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Object Perception as Bayesian Inference

Feature detection and letter identification.

Measuring the dependence of visual sensitivity on parameters of the visual stimulus is a mainstay of vision science. However, it is not widely appreciated that visual sensitivity is a product of two factors that are each invariant with respect to many properties of the stimulus and task. By estimating these two factors, one can isolate visual processes more easily than by using sensitivity measures alone. The underlying idea is that noise limits all forms of communication, including vision. As an empirical matter, it is often useful to measure the human observer’s threshold with and without a noise background added to the display, to disentangle the observer’s ability from the observer’s intrinsic noise. And when we know how much noise there is, it is often useful to calculate ideal performance of the task at hand, as a benchmark for human performance. This strips away the intrinsic difficulty of the task to reveal a pure measure of human ability. Here we show how to do the factoring of sensitivity into efficiency and equivalent noise, and we document the invariances of the two factors.

Why use noise

Do we recognize common objects by parts, or as wholes? Holistic recognition would be efficient, yet people detect a grating of light and dark stripes by parts. Thus efficiency falls as the number of stripes increases, in inverse proportion, as explained by probability summation among independent feature detectors. It is inefficient to detect correlated components independently. But gratings are uncommon artificial stimuli that may fail to tap the full power of visual object recognition. Familiar objects become special as people become expert at judging them, possibly because the processing becomes more holistic. Letters and words were designed to be easily recognized, and, through a lifetime of reading, our visual system presumably has adapted to do this as well as it possibly can. Here we show that in identifying familiar English words, even the five most common three-letter words, observers have the handicap predicted by recognition by parts: a word is unreadable unless its letters are separately identifiable. Efficiency is inversely proportional to word length, independent of how many possible words (5, 26 or thousands) the test word is drawn from. Human performance never exceeds that attainable by strictly letter- or feature-based models. Thus, everything seen is a pattern of features. Despite our virtuosity at recognizing patterns and our expertise from reading a billion letters, we never learn to see a word as a feature; our efficiency is limited by the bottleneck of having to rigorously and independently detect simple features.

The remarkable inefficiency of word recognition

A commonly used experimental paradigm for studying human information processing asks subjects to classify two stimuli with respect to their similarities and differences. The "same"-"different" judgment task, in particular, has useful applications in a variety of studies. The interpretation of "same"-"diiferent" reaction time data, however, is complicated by the existence of two seemingly anomalous effects, the fast-"same" effect and the criterion effect. This article examines explanations of these effects and brings evidence from the literature to bear on them. Current models of "same"-"different" judgments, two of which are widely accepted, can be rejected on the evidence of data reviewed here. Among the disconfirming data are several results that offer suggestions both for improving current models and for questioning some of their fundamental presuppositions. Sameness and difference are fundamental cognitive relations that enter, at least implicitly, into most forms of adaptive perceptual behavior. Accordingly, experimental tasks requiring subjects to discriminate sameness and difference among stimulus patterns have become standard investigative tools in a number of areas of psychological research, areas ranging from basic psychophysics and stimulus coding to concept learning and language processing. The time taken to make a "same"-"different" judgment has been a particularly useful measurement because reaction times (RTs) can often be used to isolate mental processes underlying phenomena of interest (Sternberg, 1969).' Aside from its methodological use as an adaptable and sensitive probe of extrinsic phenomena, the "same"-"different" judgment task has itself been the subject of considerable study over the past 15 years. The resulting body of empirical evidence has produced substantial agreement on the functional significance of information-processing operations that subserve perceptual comparisons. However, a debate, contentious at times and still unresolved, has surrounded "same"-"different" judgment

"Same"–"different" judgments: A review of current controversies in perceptual comparisons.

WE have colour vision because there are three types of cone photoreceptors which are maximally sensitive in the long (L), middle (M) and short (S) wavelength regions of the spectrum. Psychophysical experiments have, however, revealed mechanisms selectively responsive to light modulated in three 'cardinal directions' in colour space1. The responses of these mechanisms are determined by algebraic sums of the excitations of the cones. One of these mechanisms is responsive to changes in luminance, its spectral sensitivity being that of the sum of the L and M cones. The other two respond best to isoluminant changes in light. The responses of one of these mechanisms are determined by the difference in the excitations of the L and M cones, and those of the other one determined by the difference between the excitation of the S cones on the one hand and the excitations of the L and M cones on the other. We have obtained quite surprising results concerning the role of these mechanisms in the perception of motion. Drifting gratings modulated along different cardinal directions appear to slip with respect to one another. In contrast, when the directions of the modulations are rotated by 45° in colour space, the gratings cohere. Our results are consistent with the notion that information about movement is analysed within mechanisms maximally responsive along the cardinal directions.

Bart Farell

Papers

Feature detection and letter identification.

Why use noise

The remarkable inefficiency of word recognition

"Same"–"different" judgments: A review of current controversies in perceptual comparisons.

Influence of colour on the perception of coherent motion.