Psychophysics

Quantitative study of the relationship between controlled physical stimuli and sensory performance or reports.

An approximate regime in which a threshold increment is proportional to background intensity, so $\Delta I/I$ is roughly constant. It is a task- and range-dependent empirical relation, not a universal law at photon-limited levels or under all adaptation states.

A transient change in electrical conductance of the skin, often used as an index of autonomic arousal. Electrode recordings provide a physiological response measure, not a direct reading of threat beliefs or diagnostic status.

A judgment of which of two events occurred first or second. Changing the response rule, modality reliability or attention can alter measured order without implying a corresponding change in physical stimulus timing.

A judgment of whether two events occurred together. Its response curve across onset differences depends on timing noise and acceptance criteria; it need not equal the psychometric function of temporal order.

Let internal timing difference be $D=\delta +b+\epsilon$ with $\epsilon \sim N(0,s^2)$, and report simultaneous when $-h<D<h$. Standardizing the two interval bounds gives $P(\mathrm{same})=\Phi ((h-\delta -b)/s)-\Phi ((-h-\delta -b)/s)$. For positive $h,s$ and symmetric noise, this function peaks at $\delta =-b$. Its width reflects both noise and acceptance bounds, so it cannot identify a sensory window without additional assumptions.

An offset at which events are judged most simultaneous under a specified measurement procedure. A fitted peak in simultaneity reports need not coincide with the equal-response point of an order task or with equal neural onset latencies.

Measurement of gaze direction or fixations using a specified recording method and calibration procedure. Prespecified regions of interest, usable-data criteria and time windows are needed to connect gaze records to a developmental hypothesis.

An experimental method using the duration of looking as a dependent measure. A difference can reflect novelty, familiarity, surprise or processing demands, so psychological interpretation depends on the design and controls rather than on duration alone.

Presenting outcomes predicted to be congruent or incongruent with a proposed expectation and comparing looking responses. In false belief research, manipulating an agent’s visual access while controlling actual object location helps distinguish belief-based predictions from direct reality tracking. Longer looking is an indirect measure requiring alternative explanations to be tested.^[ref]

A central attention cue precedes a side cue and an auditory stimulus. The infant’s orientation controls or indexes the duration of exposure, permitting comparison of responses to stimulus classes. Masking sound for adult observers helps reduce inadvertent cueing.^[ref]

Assigning a perceptual contribution to an available response scale because a more appropriate scale is absent or unclear. An odor contribution rated only on a sweetness scale could therefore affect the score without establishing a separate gustatory sensation. Providing multiple scales and independent discrimination tests can help test this possible explanation; their results should not be presumed in advance.

A task requiring selection between two specified alternatives, such as which of two intervals contained a signal. For balanced alternatives and no usable information, expected correct performance is one half. Its decision assumptions and possible response biases must still be specified; forced choice does not remove every source of bias.

A framework separating stimulus discriminability from decision criterion in noisy tasks. Response bias and sensory sensitivity need not change together.

The ability to discriminate stimulus classes, conceptually distinct from the decision criterion determining which response is selected. A higher frequency of fear judgments can reflect a criterion shift without better discrimination.

Under an equal-variance Gaussian evidence model, $d^{\prime }$ is separation of signal and noise means in units of their common standard deviation. A yes/no task gives $d^{\prime }={\Phi }^{-1}(H)-{\Phi }^{-1}(F)$, where $H$ and $F$ are hit and false-alarm probabilities. This formula assumes the model; it does not define every possible sensory-discrimination measure.

Compare independent Gaussian samples $R_s,R_n$ with means ${\mu }_s,{\mu }_n$ and common variance ${\sigma }^2$. Choosing the larger is correct when $R_s-R_n>0$. The difference has mean ${\mu }_s-{\mu }_n$ and variance $2{\sigma }^2$, so standardization proves the displayed relation. Correlated samples, unequal variances or a different response rule need a different calculation.

A rule or boundary converting internal evidence into a response, such as reporting a signal when $R>c$. Changing the criterion can change hits and false alarms without changing the separation of the underlying evidence distributions. A measured response threshold is therefore not automatically a pure measure of sensory sensitivity.

A function relating a stimulus variable to measured response probability or discrimination performance.

An empirical psychometric function whose core $F$ ranges from zero to one, lower asymptote is $\gamma$, and upper asymptote is $1-\lambda$. If $F(\alpha )=1/2$, then $p(\alpha )=\gamma +(1-\gamma -\lambda )/2$. A location parameter is consequently not a task-independent threshold. For a two-choice observer randomly guessing on fraction $r$ of otherwise perfect easy trials, the upper error asymptote is $r/2$, not $r$.

Let internal evidence be $R=\mu (x)+\epsilon$ with zero-mean Gaussian noise of standard deviation $\sigma$, and respond yes when $R>c$. Taking a distribution tail gives $1-\Phi ((c-\mu )/\sigma )$, which equals the displayed expression by symmetry. Its derivative is $\varphi ((\mu -c)/\sigma ){\mu }^{\prime }(x)/\sigma$. Thus sensory gain, variability and criterion all influence the observed relation, and a sigmoid in one stimulus coordinate need not remain symmetric in another.

A stimulus value corresponding to a specified performance criterion in a specified task. It is a summary of a psychometric function, not a claim that every trial below that value has no sensory response. State the response definition, chance level, lapse convention and performance criterion.