Fig 1.
General structure of an alarm signal as recommended by the 2020 updated standard.
The priority pointer is used to discriminate between the different urgency priorities (low, medium, and high). The auditory icon represents the alarm category.
Fig 2.
The HP pointer burst is composed of two identical five-pulse blocks separated by 190 ms, totaling 1110 ms of duration.
HP pulses of 50 ms duration are repeated in the schematized rhythm pattern (top). The MP pointer burst has a total duration of 595 ms. MP pulses of 155 ms duration are repeated in the schematized rhythm pattern. The HP burst has a faster and uneven rhythm, features that are associated with a higher urgency perception.
Fig 3.
Spectral components of the HP (top) and MP (bottom) pulses.
Spectral centroid frequency is represented by the vertical dashed line. Both pulses conform to the updated standard suggestion of having five peaks in the 150 Hz to 4000 Hz range, and with the HP signal being higher pitched than the MP.
Fig 4.
SpO2 generic beep recorded signal representation in time domain (top) and frequency domain (bottom).
The 44100 Hz sample rate recording was done by one of the authors using a handheld recorder. The signal shows a fundamental at 1455 Hz, and two additional harmonic components of lower energy. Also visible are the longer rise and fall times than those of the priority pulses.
Fig 5.
Plots of the Grand average of the waveforms of factor (component) loadings in response to each priority at the location of the maximum peak (FCz).
Temporal factors identified as MMN and P3a are highlighted in bold solid and dashed lines respectively.
Table 1.
Temporal PCA factors: All the factors identified are ordered by the explained variance, with their latency (ms), maximum negative and positive locations and peak polarity.
The factors with the event-related potential (ERP) components of interest for the study (MMN and P3a) are included in the final column.
Fig 6.
Plots of the Grand average of ERP (dashed line) versus Temporal Factor 3 and 4 of PCA identified as MMN (regular solid line) and P3a (bold solid line) respectively, for each priority at the location of the maximum peak (FCz).
Fig 7.
(a) MMN (TF03) waves for high priority (blue lines) and medium priority (red lines) pulses of the fronto-central and central regions; and (b) voltage topographical distributions to the peak of the MMN (198 ms) in response to the high priority and medium priority pulses (* p < .05).
Fig 8.
(a) P3a (TF04) waves for high priority (blue lines) and medium priority (red lines) pulses of the Antero-Frontal, Frontal and Fronto-Central regions; and (b) voltage topographical distributions to the peak of the P3a (273 ms) in response to the High priority and Medium priority pulses (** p < .01).
Table 2.
RT and accuracy behavioural data by condition (short length and full length).