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Quantitative Measurement And Assessment Of Performance
Published in Raymond V. Smith, John H. Leslie, Rehabilitation Engineering, 2018
During sensory tests (e.g., touch, vibration, temperature, and two-point discrimination), the subject is presented with computer-controlled, precisely generated stimuli. The threshold level at which the subject is able to correctly identify the presence or absence of a stimulus 50% of the time is determined with the two-alternative, forced-choice method.31
Psychoacoustic methods
Published in Stanley A. Gelfand, Hearing, 2017
Until now, we have focused for the most part on a “yes/no” testing approach; however, other formats are used as well, and are actually more commonly employed in actual experiments. These approaches involve forced-choice paradigms in which the subject is presented with two or more alternatives from which he must choose a response. Suppose, for example, that we want to find out whether a subject can hear a tone in the presence of a noise. In a “yes/no” experiment the subject hears one stimulus presentation, which might be just a tone, or perhaps a noise alone versus a tone-plus-noise combination. In either case, the subject's task is to indicate whether the tone was there are not (“yes” or “no”). In a two-alternative forced-choice (2AFC) method, the subject is presented with two stimuli in succession, only one of which contains the tone. After listening to both stimuli, he must decide whether the tone was present in the first one or the second. Similarly, in a 4AFC experiment the subject must decide which of four successive stimuli includes the tone. Because the two or more presentations occur as successive intervals, we could also say that the subject must decide which interval contained the stimulus. Therefore, these experiments are often called two- (or more) interval forced-choice methods (hence, 2-IFC, 3-IFC, etc.). These topics are covered further in the context of signal detection theory in the next chapter.
Sensory testing and clinical neurophysiology
Published in Harald Breivik, William I Campbell, Michael K Nicholas, Clinical Pain Management, 2008
Ellen Jørum, Lars Arendt-Nielsen
There are two different methods of thermal sensory testing that are generally available: the two-alternative forced choice method and the method of limits. The two-alternative forced choice method implies that a stimulus at a given level of intensity is presented to the patient during only one of a pair of stimulus events and the patient has to indicate which of the stimuli is perceived. Success or failure at this level results in subsequent stimuli being delivered at lesser or greater stimulus intensities respectively.26 The forced choice method reduces the response bias and therefore seems better suited for a psychophysical examination, but the method is timeconsuming. The method has mainly been employed in the evaluation of neurological patients with sensory deficits in general and not in pain patients in particular. For the evaluation of pain patients, the method of limits, in which the intensity of stimulation is continuously increased from 0 (or from skin temperature) to the point of detection threshold, is probably the most appropriate. This is mainly because of ethical considerations as a suprathreshold stimulus may evoke severe pain, which is often sustained. For the same reason, it is desirable to use as few stimuli as possible to determine a pain threshold. The pain tolerance threshold may also be determined; however, for some patients, the detection threshold itself will represent the level of tolerance. For cold and heat detection thresholds, it is usual to use a total of 5–10 repeated tests, whereas for cold and heat pain three repeated measurements are often used.
Good Visual Performance Despite Reduced Optical Quality during the First Month of Orthokeratology Lens Wear
Published in Current Eye Research, 2020
Ruijing Xia, Binbin Su, Hua Bi, Jiaze Tang, Zhiyi Lin, Bin Zhang, Jun Jiang
Santolaria et al.20 studied the light distortion after orthokeratology with psychophysics results reported by yes/no procedure, which could be influenced by variations in criterion, especially in children.29 In this current study, a temporal two-alternative, forced choice paradigm was used, and the guessing rate of the subjects was controlled at 50%. In a 3-down-1-up staircase test, a subject might get extra cues from the changing trend of the stimulus. An increasing or no-change in difficulties level indicates a correct decision in the previous trial and a decreasing trend indicates incorrect decisions in the prior trials. To reduce the bias induced by presenting stimuli sequentially, two sets of staircase trials starting from different values were intertwined. The reliability could also be seen from the fact that, not only the mean values of SDT were very similar before and after lens wear, the standard deviations were also very close to each other (8.39 arcsec, 9.39 arcsec, and 9.08 arcsec for baseline, 1 week, and 1 month after, respectively).
Visual impairments in type 1 bipolar disorder
Published in The World Journal of Biological Psychiatry, 2019
Thiago P. Fernandes, Steven M. Silverstein, Natalia L. Almeida, Natanael A. Santos
CSF assessment was performed in a quiet, comfortable and reserved room; each session of the visual measurements lasted from 30 to 45 min. Participants were encouraged to take breaks whenever they wanted to, to avoid fatigue. Before the start of the tests, instructions on the operation and tasks that individuals should perform were provided. The participants were instructed to maintain fixation on a small black fixation cross in the centre of the display monitor. A two-alternative forced-choice (2-AFC) method was used. The participants’ task was to identify, using a remote-control response box, whether the grating was presented on either the left or right side of the computer screen (Figure 1). Metropsis uses a psychometric function that estimates thresholds without interference from participant’s guessing or use of visual cues. The order of the spatial frequencies that were tested was randomised within a session.
Effect of signal processing strategy and stimulation type on speech and auditory perception in adult cochlear implant users
Published in International Journal of Audiology, 2019
Susan M. Reynolds, René H. Gifford
Musical based spectral resolution was completed using chord discrimination. Participants were presented with a two-alternative forced choice task in which they indicated if two chords they heard were “same” or “different” using a response pad. Chords were presented as dyads, triads and tetrads as major or minor chords. Fundamental frequency of each chord ranged from 220.0 to 1046.5 Hz. All 105 trials were randomised and presented for each condition with 50% of stimuli being the same and 50% of stimuli being different. The chord stimuli were delivered via direct connect at a level deemed to be most comfortable for each listener. Participants were instructed to indicate whether they would like the level of the stimulus increased or decreased and the presentation level was set accordingly.