The PAX 2 picture processing system

PAX 2 digital picture processing program written in FORTRAN - subroutine annotation

Pattern recognition- iv. sequential operations in digital picture processing

Sequential approach to digital picture processin

Perceptual Precedence in Picture Processing

One important assumption of information processing models of human perception is that such processing occurs as a sequence of events or stages which take place over time. Recent investigations (Navon 1977, 1981) have sug gested that the global aspects of a stimulus are perceived at an earlier stage in the time course of processing than are the local elements of the stimulus. Other studies (Kinchla § Wolfe 1979; Martin 1979; Hoffman 1980) have sug gested that neither global forms nor local elements are necessarily perceived prior to the other structural level, but that other factors such as the size of the stimulus, the sparcity of the local elements, and the goodness of the form in the stimulus mediate the perceptual precedence of global and local levels. Attempts to generalize the results of the above studies to real-world perception are very tentative. The nature of the stimuli used in global precedence research is markedly different from that of real-world stimuli. Pomerantz (1981) has defined two types of relationships that exist between the global and local levels in visual stimuli: In one type there is no predictive relationship between the global and local levels (i.e., their identities are independent), while the second type contains mutually predictable (dependent) global and local levels. Real-world viewing involves the processing of stimuli of the latter type, but the global precedence studies to date have all utilized stimuli with independent global and local levels. It is not known whether generalizations can be made across these two configural types with respect to the perceptual precedence of the global or local levels. The present study investigated perceptual precedence in pictorial stimuli in which the identity of global and lo cal levels were dependent on one another. Perceptual pre cedence was measured through the use of a Stroop-like inter ference task, similar to that used by Navon C1977). The task required that subjects direct their attention to either the global or local level, as cued by the experimenter prior to each trial, and then respond yes or no to the pres ence of the cued object (local level) or scene (global level). Response latencies were recorded for each trial. Half of the trials contained inconsistent global and local levels, and the interference produced by the irrelevant level was taken as evidence for the processing precedence of that level. Stimulus display size was also varied across trials. The results indicated that for small scenes, subtend ing 4° of visual angle, global precedence did occur, but for large scenes (16°) the opposite effect ( local prece dence ) was found. The pattern very closely parallels the findings of Kinchla and Wolfe (1979), using global local independent stimuli, suggesting that the relationship between the global and local levels is not critical in de termining perceptual precedence. A model was proposed in which the structural level first perceived is determined by the spatial frequency or size of the stimulus display. The model suggests that a critical sampling bandwidth exists and that the initial pro cessing of a stimulus occurs at that level whose spatial frequency falls within the bandwidth. A post-hoc examina tion of the spatial frequencies present in the stimuli used in this study suggests that the band is centered at about 4 contour changes per degree of visual angle and ranges from 2 to 8 changes per degree

Communicating hands: ERPs elicited by meaningful symbolic hand postures.

Meaningful and meaningless hand postures were presented to subjects who had to carry out a semantic discrimination task while electrical brain responses were recorded. Both meaningful and control sets of hand postures were matched as closely as possible. The ERPs elicited by meaningless hand postures showed an anteriorly distributed N300 and a centro-posteriorly distributed N400 component. The N300 probably reflects picture-specific processes, whereas the N400-effect probably reflects processing in an amodal semantic network. The scalp-distribution of the N400-effect, which is more posterior than usually reported in picture processing, suggests that the semantic representations of the concepts expressed by meaningful hand postures have similar properties to those of abstract words

Semi-automatic process partitioning for parallel computation

On current multiprocessor architectures one must carefully distribute data in memory in order to achieve high performance. Process partitioning is the operation of rewriting an algorithm as a collection of tasks, each operating primarily on its own portion of the data, to carry out the computation in parallel. A semi-automatic approach to process partitioning is considered in which the compiler, guided by advice from the user, automatically transforms programs into such an interacting task system. This approach is illustrated with a picture processing example written in BLAZE, which is transformed into a task system maximizing locality of memory reference

Breathing and affective picture processing across the adult lifespan

The present study investigated differences between healthy younger, middle-aged, and older adults in their respiratory responses to pictures of different valence and arousal. Expiratory time shortened and end-tidal PCO2 decreased with increasing arousal in all age groups; yet, compared to younger adults, older adults' overall change from baseline was smaller for expiratory time and larger for end-tidal PCO2. Contrary to their younger counterparts, older adults' inspiratory time did not shorten with increasing arousal. Inspiratory duty cycle did not covary with affective ratings for younger adults, increased with unpleasantness for middle-aged adults, and increased with arousal for older adults. Thoracic breathing increased with increasing unpleasantness only among older adults. Age had no effects on mean inspiratory flow and minute ventilation, which both augmented as arousal increased. We discuss how age effects on respiratory response magnitude and pattern may depend on age-associated biological changes or reflect age-related differences in emotional processing

XILINX BASED HARDWARE FOR PICTURE PROCESSING AND CHARACTER RECOGNITION PURPOSES

The paper deals with the development of hardware that is capable realising picture pro- cessing and character recognition algorithms. The hardware was implemented as an IBM PC peripheral card and contains up to five XILINX XC 3090 FPGA devices. Because of the on board reconfigurability of the XILINX devices the hardware allows to imple- ment several separate algorithms at different times. For evaluation the performance of the hardware the Dineen and the linger image smoothing techniques were chosen. The image smoothing techniques can be used at the pre-processing stage of the character recognition process

Digital picture processing and psychophysics: a study of brightness perception

technical reportA computer driven display system was used to study brightness contrast phenomena, in a project motivated by research in digital picture processing. The modeling approach was that of Stockham and Davidson: the visual system is modeled as the cascade of a linear system (eye optics) and a multiplicative homomorphic system?that is, a logarithmic transformation (retinal receptors), followed by a linear system (neural interaction). In order to test the linearity of neural interaction, smooth stimulus patterns were utilized, containing only a few sinusoidal components within the low frequency band, and exhibiting classical brightness contrast effects (Mach bands, simultaneous brightness contrast, Hermann grid effect). Data were collected from brightness matching experiments with these smooth patterns. The data were verified in preliminary experiments on similar patterns digitally processed by the inverse of the model, in order to obtain cancellation of the brightness contrast effects. The experimental results showed to be in agreement with Davidson's data, obtained by a fundamentally different method. This new experimental approach indicated that the hypothesis of linearity of neural interaction is justified for smooth patterns. Further studies suggested that intensity edges and contours cause strong departure from linearity. Some steps were also taken toward extending the homomorphic model for color contrast phenomena. Conclusions are drawn about the implications of these experiments in the fields of computer image processing and visual psychophysics. The advantages of computer techniques in visual experiments are presented; the applications of the homomorphic model of brightness perception to digital picture processing are reviewed, and the implications of the experimental findings are discussed

The role of anterior cingulate cortex in the affective evaluation of conflict

An influential theory of anterior cingulate cortex (ACC) function argues that this brain region plays a crucial role in the affective evaluation of performance monitoring and control demands. Specifically, control-demanding processes such as response conflict are thought to be registered as aversive signals by ACC, which in turn triggers processing adjustments to support avoidance learning. In support of conflict being treated as an aversive event, recent behavioral studies demonstrated that incongruent (i.e., conflict inducing), relative to congruent, stimuli can speed up subsequent negative, relative to positive, affective picture processing. Here, we used fMRI to investigate directly whether ACC activity in response to negative versus positive pictures is modulated by preceding control demands, consisting of conflict and task-switching conditions. The results show that negative, relative to positive, pictures elicited higher ACC activation after congruent, relative to incongruent, trials, suggesting that ACC's response to negative (positive) pictures was indeed affectively primed by incongruent (congruent) trials. Interestingly, this pattern of results was observed on task repetitions but disappeared on task alternations. This study supports the proposal that conflict induces negative affect and is the first to show that this affective signal is reflected in ACC activation