This preview shows page 1. Sign up to view the full content.
Unformatted text preview: PSYC 103
Why be sensitive to time?
• Control patterns of activity • Measure rates of occurrence Periodic timing: the ability of animals to respond at a particular time
• Circadian rhythms
• Nocturnal, diurnal, crepuscular
Interval timing: the ability of animals to respond on the basis of specific
durations Circadian rhythms
Endogenous rhythms around 24 hrs in length…about a day.
• Implicit representation of important events in the world, that can be
modified by experience
• Animals can learn about events in relation to their circadian clock
• involves different mechanism(s) than interval timing
Entrainment: process by which the underlying rhythm-generator (pacemaker) is synchronized with environmental signals -experience dependent plasticity, calibration to the world Zeitgeber: entrainment signal (light is primary cue), other stimuli work too.
Free-running rhythm: activity in the absence of any entrainment signal, generally slightly more or less than 24h Measuring Circadian rhythms Measuring Circadian rhythms
Plotting activity: the “actogram” entrainment Free-running Circadian rhythms Experiment Day Not all shifts in rhythms are the same…. Entrainment between 22-26 hr is common, but 19 or 29 hour days are unlikely. Circadian rhythms Phase response curve Light pulses given at different times induce different changes in free-running activity Circadian rhythms Phase response curve Human melatonin
Human core body temperature Time-of-day feeding
Circadian rhythms allow animals to adjust their activities to daily periodic events,
such as opportune feeding times.
e.g. hummingbirds & bees feed on open flowers in the AM Possible mechanisms:
1. Is the circadian pacemaker entrained by feeding?
2. Is a second oscillator entrained by feeding?
3. Use circadian phase (time of day)? Time of Day Feeding Activity • Rats in running wheels were fed two one-hour meals /day at 10 AM & 4 PM Bolles & Moot 1973 • Learning about feeding times can occur when animals are in light or dark cycles
• Feeding interval must be between 22-26 hours. Can’t learn if feeding is 19 or 29 h apart.
• Effect is asymmetric: 25-26h is easier than 22-23h. Suggests 2 separate food-entrainable oscillators (clocks), but other animals show
signs of learning many feed times - bees can learn 9 and birds can learn at least 4 Time and place learning
• During 3 hour periods in a 12-h day, food is
available at a different location t1 Food
here t2 • Test with open access to all feeders Interval timing
Control of behavior by arbitrary periodicities, considerably shorter than 24h “Peak” procedure: adaptation of FI (fixed interval)
schedule with “null” trials FI20 Peak procedure Weber’s law: the accuracy of
the judgment is proportional to
the magnitude of the stimulus Interval timing
• Lever press for food after a fixed duration of darkness
• Responding to other durations produces a generalization gradient Rats can be trained to remember multiple intervals Interval timing
How do animals compute intervals?
Three possible relationships between the duration of remembered time relative
to the passage of actual time Subjective time
0 Real time 60 s Subjective time
logarithmic Time left to reward
Time-left procedure Training:
• Left lever: 60s
• Right lever: 30s Testing:
• present 30 s lever at
different points in the 60 s
interval Result: A given interval of real time is
subjectively the same whether it occurs at the
beginning or end of a longer interval
Time is measured linearly Subjective time follows real-time Interval timing
How do animals compute intervals
• Subtraction of remembered and actual durations? • Computing the ratio of remembered & actual ? Bisecting the interval
• press left lever for long (12 s) tone
• press right lever for short (3s) tone
• test with intermediate duration tones
for 50% r/l resp
• If subtraction: midpoint=7.5
• If ratio: midpoint=6 Timing summary
1. Subjective time grows linearly with real time
2. Timing obeys Weber’s law: longer times are perceived and/or
remembered with greater variance than shorter times • Scalar property of timing 3. Timing is multimodal light noise Species differences:
• rats, pigeons, humans tested most extensively
• sharpness of the peaks vary, but most data suggest that all these
species time interval similarly TIME, NUMBER
AND SERIAL ORDER
CHAPTER 10 20 ...
View Full Document