جستجوی مقالات مرتبط با کلیدواژه « psychophysics » در نشریات گروه « پزشکی »

Obliging to make decisions with only limited and sometimes insufficient evidence is one of the challenges that we face. Previous studies have examined the effect of evidence on performance, confidence, and response time. The question of what leads to a decision with insufficient evidence is still shrouded in ambiguity. This research tries to find an answer by experimenting with random dot motion tasks and using behavioral modeling.

A random dot motion psychophysics experiment was designed and 10 participants were asked to indicate the direction of dots and the degree of their confidence after observing the movement of the dots. In this experiment, the duration of stimulus display was variable and, in each trial, randomly had one of the six specified durations (80 to 720 milliseconds). As the stimulus display time varied, participants were exposed to sufficient and insufficient evidence to make a decision. The results of the participants' behavioral data were analyzed by psychometric functions and the participants' behavior was modeled using the drift-diffusion model.

Our behavioral data indicate that the duration of stimulus display has a significant impact on increasing accuracy and confidence as well as on reducing response time. Behavioral modeling results also showed that the decision components (i.e., threshold separation, drift rate, and none-decision time) are affected by changes in stimulus duration, and threshold separation is significantly affected. The threshold separation increases significantly as the stimulus shows increases.

Our investigation supports the hypothesis that the brain changes the decision threshold and adapts to the situation when making decisions based on insufficient evidence.

We encounter different information or stimuli. However, the combination of these stimuli and the quality of their presentation can influence our perception and decision. Despite the importance of these combined stimuli to our judgments and decisions, it is not yet clear how the characteristics of these stimuli affect the decision- making processes. For example, it is not clear whether the time interval between the information we receive can affect the accuracy and speed of decision- making. This study aimed to investigate the effect of the time interval between two different visual stimuli on perceptual decision- making.

According to psychophysical experiments, it was possible to measure the response to perceptual stimuli and compare perceptual choices. In a Random Dot Motion (RDM), the task was displayed to the participants as the primary visual stimulus and a graphic cue as the second visual stimulus, at different intervals, and then the participant's decision accuracy and reaction time to each of these two stimuli were recorded and analyzed.

We found that in RDM (primary stimulus), the accuracy of participants' decisions is not affected by the time interval between the presentation of two stimuli. Instead, the accuracy of the response to the Cue (second visual stimulus) decreases in long time intervals between two stimuli. Interestingly, if two stimuli are presented simultaneously, the decision about each of these stimuli is reasonably accurate; yet, the speed of the decision- making process is slower than when a person encounters two stimuli separated by a time interval.

The human visual system can distinguish visual stimuli that are presented with a short time interval in between; however, in exchange for correctly identifying these stimuli, the speed of decision- making may be slowed down.

Human visual system is able to recognize the objects relevant information in natural images rapidly and efficiently. In the recognition process, an object can belong to different levels of abs traction (superordinate, basic, and subordinate) in a hierarchical s tructure. However, it remains unclear whether different ques tions at levels of object categorization for identical s timulus create different activation responses in the brain or not.
In order to inves tigate the relation between brain function and human behavior, three behavioral experimental s tudies have been designed with help of psychophysics’ toolbox in MATLAB R2015a. During these experiments, the participants asked to record animate, face, and animal face images as target images respect to the superordinate, basic, and subordinate levels, respectively. The experiments include seven blocks of 96 trials in superordinate (four blocks), basic (two blocks), and subordinate (one block) levels. Totally each subject has done 672 trials.
We observed that subjects’ reaction time were task dependent for the same images in contras t to previous s tudies. That is, images in the superordinate level were observed in the early component of reaction time whereas basic and subordinate levels emerged relatively late. In all levels, only a set of 48 target images (animal face) was analyzed. These target images were randomly mixed with other ones.
The results showed that superordinate level is well separated from the other two levels. In other words, this level needs more general information for object recognition process than other levels. These findings sugges t that categorization of objects at different levels has done by three dis tinct neuronal circuits. Moreover, these results indicate that there are some top-down signals which change the information processing path respect to the ques tions.

Most decisions are based on the accumulation of discrete pieces of evidence. This evidence has usually been separated with the various intervals. Indeed, how the brain gathers and combines distinct pieces of information received at different times is need to be clarified. In order to investigate the kinship between brain function and human behavior, the behavioral experimental studies could be designed. Previous studies demonstrated that subjects gather and effectively combine discrete evidence to improve their accuracy. In addition, it has been shown that the latest information has a larger influence on decisions. However, it remains unclear that why this larger influence of the later pulses occurs and what can affect this influence.
Dealing with these questions a perceptual decision-making task has been implemented by the psychophysics’ toolbox in MATLAB. Subjects, during the task, were instructed to report the direction of motion in a noisy random dot stimulus with certain keys. Stimuli were presented in continuous (one pulse) or discrete (two continuousness pulses separated with different intervals) form. Each of these two forms of stimuli was presented randomly during each session. Each session has been included 300 trials. Each subject has done 3600 trials. Data have been analyzed by regression models.
We observed that in double-pulse trials, the strength of the second pulse was more crucial in the accuracy of responses compared to the first pulse. In addition, this accuracy was dependent on the differences between the strength of the first and the last pulses.
These findings suggest that a key factor which affects the importance of pulses is the strength of the previous pulse. As the difference between the motion strength increases, the effect of the second pulse on choice accuracy enhanced.

Decision process is an accumulation-to-bound mechanism, in which momentary sensory evidence is accumulated over time toward a criterion level. This bounded evidence accumulation is represented in the activity of neurons in the lateral intraparietal (LIP) cortex. Whether the firing rate of LIP neuron contains post decision information (PDI) or returns to baseline level as soon as decision made needs to be clarified.
To investigate this issue, we conducted behavioral experiments based on the two forced-choice discrimination of motion direction. Human subjects reported the net direction of stochastic random dot motion by pressing a key of specified keys associated with the two possible directions of motion. Trials were separated by different time gaps.
Results showed that there is a preference in subjects to make a same decision as their pervious decision, especially in weak stimuli.
Our findings suggest that the value of decision variable (DV) after crossing the bound (named PDI) may accumulate with DV for the next decisions.